Method for producing hydrogels coupling high elastic modulus and absorbance

ABSTRACT

The present invention provides crosslinked carboxymethylcellulose having high elastic modulus coupled with high absorbance capacity when swollen in simulated gastric fluid/water (1:8) and simulated intestinal fluids. The invention further provides methods of making the crosslinked carboxymethylcellulose, compositions comprising the crosslinked carboxymethylcellulose and methods of using the crosslinked carboxymethylcellulose, for example, for treating overweight or obesity or for enhancing glycemic control.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/109,392, filed on Jan. 29, 2015. The entire teachings of the aboveapplication are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Polymer hydrogels are crosslinked hydrophilic polymers which are capableof absorbing and retaining large amounts of water. Certain of thesematerials are capable of absorbing over 1 kg of water per gram of drypolymer. The cross-links between the macromolecular chains form anetwork which guarantees the structural integrity of the polymer-liquidsystem and prevents the complete solubilisation of the polymer whileallowing the retention of the aqueous phase within the molecular mesh.Polymer hydrogels having a particularly large capacity to retain waterare referred to as superabsorbent polymer hydrogels (SAPs). Highabsorbency under load (AUL) is also a common characteristic of SAPswhich in general is not displayed by polymer hydrogels having lowercapacity to retain water. In addition to pressure, pH and otherenvironmental conditions can affect the water retainment capacity of apolymer hydrogel, such as a SAP. Applications of highly absorbentpolymer hydrogels include as absorbent cores in the field of absorbentpersonal hygiene products (Masuda, F., Superabsorbent Polymers, Ed.Japan Polymer Society, Kyoritsu Shuppann, (1987)) and as devices for thecontrolled release of water and nutrients into arid soils.

Carboxyalkyl cellulose materials and other carboxyalkyl polysaccharidesare known in the art. Carboxyalkyl cellulose materials can be formed bytreating a cellulosic material with a carboxyalkylating agent, such as achloroalkanoic acid, usually monochloroacetic acid, and an alkali, suchas sodium hydroxide, optionally in the presence of an alcohol. Suchcarboxyalkyl celluloses are generally water-soluble. Various methods ofrendering such water-soluble carboxyalkyl celluloses water-insoluble areknown. However, these methods rely on a stabilization mechanism whichdoes not include the use of any cross-linker; the procedure involvesselecting a proper range of temperature and heat treating time totransform the water soluble cellulose derivative into a non-watersoluble form. The resulting stabilization appears to be mainly due tophysical rather than chemical effects. In fact, at certain pH values,generally from about pH 10 and higher, the cellulose derivatives becomewater soluble again. (Flory, J. P. Principles of Polymer Chemistry;Cornell University: Ithaca, N.Y., 1953).

Other methods for the insolubilization of carboxyalkyl cellulosematerials include the heat treatment of the carboxyalkyl cellulose inthe presence of excess carboxyalkylating reactants and by-products ofthe carboxyalkylation reaction, to provide a water-insolublecarboxyalkyl cellulose having desirable liquid absorption and retentionproperties and characteristics. In these cases, the use of acceleratorsand catalysts to promote the stabilization (i.e., permanentcross-linking), coupled to a nonuniform distribution of the degree ofcross-linking, result in an insoluble material having a low swellingcapacity (Anbergen U., W. Opperman, Polymer, 31, 1854 (1990), Nijenhuis,K. te, Advances in Polymer Science, 130, (1997)).

Cellulose-based hydrogels can be obtained via either physical orchemical stabilization of aqueous solutions of cellulosics. Additionalnatural and/or synthetic polymers have been combined with cellulose toobtain composite hydrogels with specific properties [Chen, H.; Fan, M.Novel thermally sensitive pH-dependent chitosan/carboxymethylcellulosehydrogels. J. Bioact. Compat. Polym. 2008, 23 (1), 38-48. Chang, C.;Lue, A.; Zhang, L. Effects of cross-linking methods on structure andproperties of cellulose/PVA hydrogels. Macromol. Chem. Phys., 2008, 209(12), 1266-1273] (A. Sannino, M. Madaghiele, F. Conversano, A.Maffezzoli, P. A. Netti, L. Ambrosio and L. Nicolais' “Cellulosederivative-hyaluronic acid based microporous hydrogel crosslinkedthrough divinyl sulfone (DVS) to modulate equilibrium sorption capacityand network stability”, Biomacromolecules, Vol. 5, No. 1 (2004) 92-96).Physical, thermoreversible gels are usually prepared from watersolutions of methylcellulose and/or hydroxypropyl methylcellulose (in aconcentration of 1-10% by weight) [Sarkar, N. Thermal gelationproperties of methyl and hydroxypropyl methylcellulose. J. Appl. Polym.Sci., 1979, 24 (4), 1073-1087]. The gelation mechanism involveshydrophobic associations among the macromolecules possessing the methoxygroup. At low temperatures, polymer chains in solution are hydrated andsimply entangled with one another. As temperature increases,macromolecules gradually lose their water of hydration, untilpolymer-polymer hydrophobic associations take place, thus forming thehydrogel network. The sol-gel transition temperature depends on thedegree of substitution of the cellulose ethers as well as on theaddition of salts. A higher degree of substitution of the cellulosederivatives provides them a more hydrophobic character, thus loweringthe transition temperature at which hydrophobic associations take place.A similar effect is obtained by adding salts to the polymer solution,since salts reduce the hydration level of macromolecules by recallingthe presence of water molecules around themselves. Both the degree ofsubstitution and the salt concentration can be properly adjusted toobtain specific formulations gelling at 37° C. and are thus potentiallyuseful for biomedical applications [Tate, M. C.; Shear, D. A.; Hoffman,S. W.; Stein, D. G.; LaPlaca, M. C. Biocompatibility ofmethylcellulose-based constructs designed for intracerebral gelationfollowing experimental traumatic brain injury. Biomaterials, 2001, 22(10), 1113-1123. Materials, 2009, 2, 370 Chen, C.; Tsai, C.; Chen, W.;Mi, F.; Liang, H.; Chen, S.; Sung, H. Novel living cell sheet harvestsystem composed of thermoreversible methylcellulose hydrogels.Biomacromolecules, 2006e7 (3), 736-743. Stabenfeldt, S. E.; Garcia, A.J.; LaPlaca, M. C. Thermoreversible laminin-functionalized hydrogel forneural tissue engineering. J. Biomed. Mater. Res., A 2006, 77 (4),718-725.]. However, physically crosslinked hydrogels are reversible [TeNijenhuis, K. On the nature of cross-links in thermoreversible gels.Polym. Bull., 2007, 58 (1), 27-42], and thus might flow under givenconditions (e.g., mechanical loading) and might degrade in anuncontrollable manner. Due to such drawbacks, physical hydrogels basedon methylcellulose and hydroxypropylmethylcellulose (HPMC) are notrecommended for use in vivo.

As opposed to physical hydrogels which show flow properties, stable andstiff networks of cellulose can be prepared by inducing the formation ofchemical, irreversible cross-links among the cellulose chains. Eitherchemical agents or physical treatments (i.e., high-energy radiation,thermal crosslinking) can be used to form stable cellulose-basednetworks. The degree of cross-linking, defined as the number ofcross-linking sites per unit volume of the polymer network, affects thediffusive, mechanical and degradation properties of the hydrogel, inaddition to the sorption thermodynamics, and can be controlled to acertain extent during the synthesis. Specific chemical modifications ofthe cellulose backbone might be performed before cross-linking, in orderto obtain stable hydrogels with given properties. For instance,silylated HPMC has been developed which cross-links through condensationreactions upon a decrease of the pH in water solutions.

As a further example, tyramine-modified sodium carboxymethylcellulose(NaCMC) has been synthesized to obtain enzymatically gellableformulations for cell delivery [Ogushi, Y.; Sakai, S.; Kawakami, K.Synthesis of enzymatically-gellable carboxymethylcellulose forbiomedical applications. J. Biosci. Bioeng., 2007, 104 (1), 30-33].Photocrosslinking of aqueous solutions of cellulose derivatives isachievable following proper functionalization of cellulose. However, theuse of chemical cross-linker and/or functionalizing agents provides aproduct which is not suitable for oral administration, especially insignificant amounts and chronic use.

SUMMARY OF THE INVENTION

The present invention relates in part to the discovery that chemicalcross-linking of high viscosity carboxymethylcellulose having a lowpolydispersity index results in the formation of crosslinkedcarboxymethylcellulose having significant absorption properties,rheological properties and other advantageous characteristics.

The present invention provides processes for producing crosslinkedcarboxymethylcellulose comprising cross-linking high viscositycarboxymethylcellulose. The invention further relates to the crosslinkedcarboxymethylcellulose produced using these processes. Thesecross-linked carboxymethylcelluloses have both a high elasticity modulusand high absorption capacity as described further herein. In fact, thecross-linked carboxymethycelluloses of the invention have significantlygreater elasticity but similar absorption properties when compared toprior art crosslinked carboxymethylcelluloses. This is surprising inthat an increase in elasticity is typically accompanied by a decrease inabsorption properties (Flory J. P., “Principles of Polymer Chemistry”,Cornell University Press, Ithaca N. Y., (1953); Peppas L. B. and HarlandR. S. in “Absorbent Polymer Technology” Ed by L. B. Peppas, ElsevierPub., Amsterdam (1990); F. L. Buchholz and N. A. Peppas SuperabsorbentPolymers, Eds., ACS Symposium Series 573, Washington, D.C., 4, p. 50(1994)).

In one embodiment the invention provides a method of producing acrosslinked carboxymethylcellulose comprising the step of crosslinking ahigh viscosity carboxymethylcellulose with citric acid. The methodfurther provides the crosslinked carboxymethylcelluloses produced bythis method. Preferably, the high viscosity carboxymethylcellulose iscrosslinked with an amount of citric acid from about 0.05% to about 0.5%by weight relative to the weight of the carboxymethylcellulose.

In one embodiment, the invention provides the method of producing acrosslinked carboxymethylcellulose comprises the steps of (1) preparingan aqueous solution of high viscosity carboxymethylcellulose and citricacid; (2) optionally agitating the solution, for example, by stirring;(3) isolating a carboxymethylcellulose/citric acid composite from thesolution and (4) heating the carboxymethylcellulose/citric acidcomposite at a temperature of at least about 80° C., therebycross-linking the carboxymethylcellulose with the citric acid. In oneembodiment, the carboxymethylcellulose/citric acid composite iscomminuted prior to conducting step (4). In one embodiment, thecarboxymethylcellulose/citric acid composite is heated in step (4) to atemperature of about 80° C. or higher. The method further optionallyincludes the steps of (5) washing the crosslinked carboxymethylcelluloseof step (4) and (6) comminuting the washed crosslinkedcarboxymethylcellulose.

The aqueous solution of carboxymethylcellulose and citric acid ispreferably prepared by adding the carboxymethylcellulose and the citricacid to water and agitating, for example by stirring, the resultingmixture for a sufficient amount of time to create a homogenous solution.

The high viscosity carboxymethylcellulose is preferably present in thesolution of step (1) in a concentration of at least about 1% by weightrelative to water, preferably at least about 2%, 4% or 5%. In oneembodiment, the concentration of the carboxymethylcellulose is about 6%by weight relative to water. In certain embodiments, thecarboxymethylcellulose concentration is from about 2% to about 10%,about 4% to about 8%, from about 4.5% to about 7.5%, from about 5% toabout 7%, or from about 5.5% to about 6.5% by weight relative to water.

The citric acid is preferably present in the solution of step (1) at aconcentration of about 0.05% to about 0.5% by weight relative to thecarboxymethylcellulose. More preferably, the citric acid is present in aconcentration of about 0.1% to 0.5%; 0.4% or less; or 0.35% or less byweight relative to the carboxymethylcellulose. In an embodiment, thecitric acid is present in the solution of step (1) in a concentration ofabout 0.15% to about 0.4%, about 0.15% to about 0.35%, 0.2% to about0.35%, about 0.25% to about 0.35%, or about 0.2% by weight relative tothe carboxymethylcellulose.

In one embodiment, the aqueous solution consists essentially of highviscosity carboxymethylcellulose, for example, as the sodium salt,citric acid and water. In a preferred embodiment, the solution consistsessentially of high viscosity sodium carboxymethylcellulose, citric acidand water. The water is preferably purified water, such as distilled ordeionized water. In this embodiment, the process is conducted in thesubstantial absence of any other agent that may affect the pH.

The cross-linking reaction is preferably conducted in the substantialabsence of a catalyst.

In another embodiment, the invention provides a crosslinkedcarboxymethylcellulose produced by the methods disclosed herein. Suchcrosslinked carboxymethylcelluloses include citric acid crosslinkedcarboxymethylcelluloses having a high elastic modulus and a high mediauptake ratio when determined as set forth herein. The crosslinkedcarboxymethylcellulose of this invention are additionally relativelyinsensitive to the high ionic strength of intestinal fluid. Couplinghigh sorption capacity to high elastic modulus is advantageous for anumber of applications of these materials in therapies directed to thegastrointestinal tract, such as treatment of obesity and glycemiccontrol. Without being bound by theory, a swollen hydrogel in the upperGI tract with elasticity better coupling the one of the ingested foodwould be expected to increase stomach emptying times and elasticresponse on stomach walls. Moreover, in the lower GI tract, higherelasticity of a swollen hydrogel may slow down the glucose trafficking,reducing glycemic peaks, in addition to generating a better bulkhindrance in the intestine. In the lower GI, partially digested foodhaving high elasticity and bulk has been demonstrated to play afundamental rule in metabolic pathways promoting weight loss (Saeidi N.et al., Science 2013, 341(6144):406-10). Thus, the crosslinkedcarboxymethylcellulose of the invention is expected to treat obesity andenhance glycemic control via multiple mechanisms.

In another embodiment, the invention provides methods of using thecrosslinked carboxymethylcellulose of the invention, for example forreducing calorie intake, reducing weight or treating obesity in asubject in need thereof. The invention also provides methods of usingthe crosslinked carboxymethylcellulose of the invention in methods ofenhancing glycemic control, treating diabetes or preventing diabetes ina subject in need thereof. Additional, the invention providespharmaceutical compositions and articles of manufacture comprising acrosslinked carboxymethylcellulose of the invention.

BRIEF SUMMARY OF THE DRAWINGS

FIG. 1 illustrates the proposed mechanism of cross-linking of acellulosic polymer by citric acid.

FIG. 2 is a graph showing the dialysate glucose concentration for testsperformed with Hydrogel A and Hydrogel B as a function of time asdescribed in Example 6.

FIG. 3 is a graph of media uptake ratio (MUR) versus time followingcapsule disintegration for Hydrogel A and Hydrogel B as described inExample 7.

FIG. 4 is a graph of viscosity versus time for Hydrogel A and Hydrogel Bas described in Example 8.

FIG. 5 is a graph of media uptake ratio versus time for Hydrogel A andHydrogel B as described in Example 8.

FIG. 6 is a graph of G′ versus time for Hydrogel A and Hydrogel B asdescribed in Example 8.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides crosslinked carboxymethylcellulose,methods of producing the crosslinked carboxymethylcellulose, methods ofuse of the crosslinked carboxymethylcellulose and articles ofmanufacture comprising the crosslinked carboxymethylcellulose. Incertain embodiments, the invention relates to the discovery thatchemically crosslinking high viscosity carboxymethylcellulose providescrosslinked carboxymethylcellulose having advantageous properties.

The high viscosity carboxymethylcellulose can be chemically crosslinkedusing a suitable polyfunctional, for example, bifunctional, crosslinkingagent which produces covalent crosslinks. Suitable crosslinking agentsinclude polycarboxylic acids, such as oxalic acid or citric acid,divinylsulphone (DVS), aldehydes, such as acetaldehyde, formaldehyde andglutaraldehyde, diglycidyl ether, diisocyanates, dimethyl urea,epichlorohydrin, oxalic acid, phosphoryl chloride, trimetaphosphate,trimethylomelamine, and polyacrolein. The carboxymethylcellulose canalso be crosslinked to itself, without the presence of the crosslinkingagent in the product. For example carboxymethylcelulose can becrosslinked in the presence of a carboxy activating agent, such as acarbodiimide, or by heat treatment. It is also possible to ionicallycrosslink or physically crosslink the carboxymethylcellulose.

Preferably, the high viscosity carboxymethylcellulose is crosslinkedwith citric acid.

In one embodiment, the method of producing a crosslinkedcarboxymethylcellulose comprises the steps of: (1) preparing an aqueoussolution of high viscosity carboxymethylcellulose and citric acid; (2)optionally agitating the solution; (3) isolating acarboxymethylcellulose/citric acid composite from the solution; and (4)heating the carboxymethylcellulose/citric acid composite at atemperature of at least about 80° C., thereby producing the crosslinkedcarboxymethylcellulose. In one embodiment, thecarboxymethylcellulose/citric acid composite is comminuted prior toconducting step (4) and optionally sieved to obtain particles of adesired size range. In one embodiment, the crosslinkedcarboxymethylcellulose product of step (4) is washed and comminuted, forexample, by grinding or milling, and optionally sieved. In certainembodiments, the carboxymethylcellulose/citric acid composite iscomminuted prior to conducting step (4) and optionally sieved to obtainparticles of a desired size range; and the crosslinkedcarboxymethylcellulose product of step (4) is comminuted to producecrosslinked carboxymethylcellulose particles, and the particles areoptionally sieved.

The carboxymethylcellulose is preferably present in the solution of step(1) in a concentration of at least about 1% by weight relative to water,preferably at least about 2%, 4% or 5%. In one embodiment, theconcentration of the carboxymethylcellulose is about 6% by weightrelative to water. In certain embodiments, the carboxymethylcelluloseconcentration is from about 2% to about 10%, about 4% to about 8%, fromabout 4.5% to about 7.5%, from about 5% to about 7%, or from about 5.5%to about 6.5% by weight relative to water.

The citric acid is preferably present in the solution of step (1) at aconcentration of about 0.05% to about 0.5% by weight relative to thecarboxymethylcellulose. Preferably, the citric acid is present in aconcentration of about 0.4% or less or 0.35% or less by weight relativeto the carboxymethylcellulose. In an embodiment, the citric acid ispresent in the solution of step (1) in a concentration of about 0.1% toabout 0.5%, 0.15% to about 0.4%, about 0.15% to about 0.35%, 0.2% toabout 0.35%, about 0.25% to about 0.35%, or about 0.2% by weightrelative to the carboxymethylcellulose.

In the methods of the invention, the carboxymethylcellulose/citric acidcomposite can be isolated from the solution by any method that avoidssubstantial deterioration of the absorption characteristics of theresulting crosslinked carboxymethylcellulose. Examples of such methodsinclude evaporative drying, freeze drying, precipitation,centrifugation, spray drying, critical point drying, and the like.

In the methods of the invention, the carboxymethylcellulose/citric acidcomposite is preferably isolated by evaporative drying at a temperaturewithin the range from about 10° C. to about 100° C., preferably fromabout 45° C. to about 80° C. In certain embodiments, drying is conductedat an initial temperature of about 80° C. or higher, for example, from80° C. to 100° C., to substantially reduce the solution volume, then thetemperature is reduced below 80° C. to complete the drying. For example,the solution can be dried initially at 85° C., and then the temperaturecan be reduced to 50° C. to complete the drying. Naturally, highertemperatures can be employed if the solution is placed under pressure.Lower temperatures can be employed if the solution is placed under avacuum. In one preferred embodiment, evaporative drying is conducted ata temperature of about 65 to 75° C. or about 70° C.

In embodiments of the methods of the invention in which the solution isdried by heating, the step of isolating thecarboxymethylcellulose/citric acid composite and the step ofcrosslinking the composite can be combined in a single step, preferablywith a temperature change.

Other methods of isolation of the composite which can be sued in themethods of the invention include precipitation in which a precipitatingagent (non-solvent), such as methanol, ethanol or acetone is added tothe aqueous solution to precipitate the composite from solution. Thecomposite can then be recovered by filtration. If precipitation is usedto recover the composite, the composite is optionally washed with waterto remove the precipitating agent.

If evaporative drying by spray drying is employed, the composite may berecovered in the form of particles, flakes or granules prior to thecross-linking step.

In one embodiment, the method of the invention includes the steps of (1)preparing an aqueous solution of high viscosity carboxymethylcelluloseand citric acid; (2) agitating the solution; (3) heating the solution toremove water and produce a carboxymethylcellulose/citric acid composite;(3a) comminuting the carboxymethylcellulose/citric acid composite toproduce composite particles; (4) heating the composite particles at atemperature of at least about 80° C., thereby cross-linking thecarboxymethylcellulose with the citric acid and forming the crosslinkedcarboxymethylcellulose; (5) washing the crosslinkedcarboxymethylcellulose; (6) drying the washed crosslinkedcarboxymethylcellulose and, optionally, (7) comminuting the crosslinkedcarboxymethylcellulose to produce crosslinked carboxymethylcelluloseparticles. The particles produced in either or both of steps (3a) and(7) can be sieved to yield a sample of particles within a specified sizerange.

One preferred embodiment of the method of the invention comprises thefollowing steps: (1), high viscosity sodium carboxymethylcellulose andcitric acid are dissolved in purified water to produce a solutionessentially consisting of about 5% to about 7%, preferably about 6%,sodium carboxymethylcellulose by weight relative to the weight of water,and citric acid in an amount of about 0.15% to about 0.40%, about 0.15%to about 0.35%, about 0.15% to 0.25% or about 0.2% by weight relative tothe weight of sodium carboxymethylcellulose; (2), maintaining thesolution at a temperature from about 40° C. to about 70° C. or 40° C. toabout 80° C., preferably about 70° C., to evaporate the water and form acarboxymethylcellulose/citric acid composite; (3), comminuting thecarboxymethylcellulose/citric acid composite to form compositeparticles; and (4), maintaining the composite particles at a temperaturefrom about 80° C. to about 150° C. or about 100° C. to about 150° C.,about 115° C. to about 125° C. preferably, about 120° C., for a periodof time sufficient to achieve the desired degree of cross-linking andform the crosslinked carboxymethylcellulose. The method can optionallyfurther include one or more of Step (5), washing the crosslinkedcarboxymethylcellulose with purified water, preferably with an amount ofpurified water from 100 to 200 times the mass of the crosslinkedcarboxymethylcellulose, preferably about 150 times the mass of thecrosslinked carboxymethylcellulose; Step (6), drying the washedcrosslinked carboxymethylcellulose at elevated temperature, preferablyfrom about 40° C. to about 70° C. or 40° C. to about 80° C., morepreferably about 70° C.; and Step (7), comminuting the dried crosslinkedcarboxymethylcellulose. In one embodiment, the resulting particles aresieved to the size range of 100 μm to 1000 μm, preferably with anaverage size in the range of 400 to 800 μm.

In another particularly preferred embodiment, the method for preparing acrosslinked carboxymethylcellulose of the invention comprises the stepsof (a) providing an aqueous solution consisting essentially of: (a) highviscosity sodium carboxymethylcellulose, citric acid and water; (b)stirring the aqueous solution; (c) evaporating the water, for example bymaintaining the solution at a temperature from about 40° C. to about 70°C. or 40° C. to about 80° C., preferably about 70° C., to form acarboxymethylcellulose/citric acid composite; (d) comminuting thecomposite to form composite particles; and (e) heating the compositeparticles to a temperature of at least about 80° C. or 100° C. forexample from 100° C. to 180° C., from 100° C. to 150° C., from 110° C.to 130° C., from about 115° C. to about 125° C. or about 120° C.,thereby cross-linking the carboxymethylcellulose and forming a citricacid crosslinked carboxymethylcellulose.

The product of step (e) is optionally comminuted to produce particleswhich are optionally sieved. In other embodiments, the product of step(e) is washed, dried and then comminuted to produce particles which areoptionally sieved. In one embodiment, the crosslinkedcarboxymethylcellulose consists substantially of particles in the sizerange from 1 μm to 2000 μm, preferably from 10 μm to 2000 μm, and morepreferably from 100 μm to 1000 μm. A sample of crosslinkedcarboxymethylcellulose consists substantially of particles in aspecified size range when the sample is greater than 50% by massparticles in the specified size range. Preferably, the sample is atleast 50%, 60%, 70%, 80%, 90% or 95% by mass particles in the specifiedsize range. More preferably the sample is at least 90 or 95% by massparticles in the size range of 100 μm to 1000 μm, preferably with anaverage particle diameter in the range of 400 μm to 800 μm.

The high viscosity sodium carboxymethylcellulose is preferably presentin the aqueous solution of step (a) at a concentration of 4% or greater,preferably from about 4% to about 8%, 5% to about 7%, 5.5% to about 6.5%or about 6% by weight relative to the weight of the water used toprepare the solution. Preferably the citric acid is present in thesolution at a concentration of about 0.5% or less, more preferably,about 0.35% or less or about 0.3% or less by weight relative to theweight of the cellulose derivative. Preferably the concentration of thecitric acid is about 0.15% to about 0.35%, preferably about 0.2% toabout 0.35%, 0.15% to about 0.3%, 0.15 to 0.25% or about 0.2% by weightrelative to the sodium carboxymethylcellulose. sodium salt.

In any embodiment of the methods of the invention, the high viscositycarboxymethylcellulose is preferably present in the aqueous solution ina concentration of about 5 to about 7%, preferably about 6 wt % relativeto the weight of the water, and the citric acid is present at aconcentration of 0.1 to 0.4%, preferably 0.15 to 0.3% by weight relativeto the weight of the carboxymethylcellulose.

In certain embodiments of the methods of the invention, the aqueoussolution is dried to form the composite as a sheet, which is comminutedto form composite particles. Preferably the composite particles have agreatest dimension between about 10 μm and about 2000 μm, morepreferably between about 100 μm and about 2000 μm, or between about 100μm and about 1600 μm with an average size of between 300 μm and 600 μm.The composite particles are optionally sieved to provide particles inthe desired size range.

In preferred embodiments of the methods of the invention, the aqueoussolution is placed in a tray prior to removing the water. The heatingpreferably is conducted in a suitable oven or vacuum oven.

In the methods of the invention, the composite can be comminuted, forexample, by grinding, milling or fragmenting, to form compositeparticles, and the particles are maintained at elevated temperature,thereby effecting cross-linking and producing crosslinkedcarboxymethylcellulose particles.

The methods of the invention can further include the step of washing thecrosslinked carboxymethylcellulose, for example, washing the crosslinkedcarboxymethylcellulose in a polar solvent, such as water, a polarorganic solvent, for example, an alcohol, such as methanol or ethanol,or a combination thereof.

In preferred embodiments of the methods of the invention, thecrosslinked carboxymethylcellulose is washed with an amount of purifiedwater which is 50 to 250-fold greater (wt/wt) than the amount of thecrosslinked polymer. In certain embodiments, the amount of purifiedwater is 100 to 200-fold greater (wt/wt) than the amount of thecrosslinked polymer. In certain embodiments, the amount of purifiedwater is about 150-fold greater (wt/wt) than the amount of thecrosslinked polymer.

The washed crosslinked carboxymethylcellulose can further be dried toremove most or substantially all water. Preferably the crosslinkedcarboxymethylcellulose is dried to a water content of about 25% byweight or less, preferably about 20%, about 15% or about 10% or less. Incertain embodiments, the water content of the dried crosslinkedcarboxymethylcellulose is about 5% or less by weight.

In one embodiment, the drying step is carried out by immersing the fullyswollen crosslinked carboxymethylcellulose in a cellulose non-solvent, aprocess known as phase inversion. A “cellulose non-solvent”, as thisterm is used herein, is a liquid compound which does not dissolvecarboxymethylcellulose and does not swell the crosslinkedcarboxymethylcellulose, but is preferably miscible with water. Suitablecellulose non-solvents include, for example, acetone, methanol, ethanol,isopropanol and toluene. Following immersion in the nonsolvent, residualnonsovent can be removed from crosslinked carboxymethylcellulose byvacuum and/or heating.

In other embodiments, the crosslinked carboxymethylcellulose is notdried by phase inversion. The washed crosslinked carboxymethylcelluloseis preferably dried by air drying, vacuum drying, freeze drying or bydrying at elevated temperature, for example, in an oven or vacuum oven.These drying methods can be used alone or in combination. Oven dryingcan be carried out at a temperature of, for example, approximately30-80° C. until the water or residual non-solvent is completely removed.The washed and dried crosslinked carboxymethylcellulose can then be usedas is, or can be comminuted and optionally sieved to produce crosslinkedcarboxymethylcellulose particles of a desired size.

In the methods of the invention, the aqueous solution of thecarboxymethylcellulose and the citric acid can be formed at anytemperature at which the carboxymethylcellulose derivative is soluble inthe water. Generally, such temperatures will be within the range of fromabout 10° C. to about 100° C. Preferably, the solution is preparedsubstantially at room temperature, for example, between 20° C. and 30°C. or about 25° C.

In any embodiment of the methods of the invention it is preferred tohave the pH of the aqueous solution of high viscositycarboxymethylcellulose and citric acid between about 5 to about 9, fromabout 5 to about 8, from about 6 to 8, from about 6 to about 7, fromabout 6.5 to about 7.5 or about 5.5 to about 7. More preferably thesolution pH is between 6 and 7.

Without being bound by theory, is believed that thecarboxymethylcellulose/citric acid composite isolated from the aqueoussolution is suitable for chemical cross-linking to form crosslinkedcarboxymethylcellulose having improved absorption properties due to theinter-chain entanglements. Without being bound by theory, it is believedthat solubilization provides for molecular entanglements which produce atighter network and a preferred distribution of the carboxyl groups andhydroxyl groups between the carboxymethylcellulose and the citric acid.Greater entanglement of the carboxymethylcellulose chains thus resultsin a more uniform cross-linking upon heat-treatment, resulting, in turnin a super-absorbent crosslinked carboxymethylcellulose with a greatermedia uptake capacity and significantly improved mechanical andrheological properties.

In methods of the invention comprising the step of comminuting thecarboxymethylcellulose/citric acid composite, the resulting compositeparticles preferably have a maximum cross-sectional diameter or greatestdimension within the range from about 5 μm to about 2,000 μm, preferablywithin the range from about 100 μm to about 1,000 μm, and morepreferably the average particle cross-sectional diameter is from about300 μm to about 800 μm.

Without being bound by theory, it is believed that the step ofcomminuting the composite prior to crosslinking provides a homogeneousdistribution of cross-linking sites as well as enhanced waterevaporation before the crosslinking reaction begins, resulting in amaterial with high conservative modulus (G′) and uniform chemicalstabilization and increasing the extent of the reaction.

In the methods of the invention, the isolatedcarboxymethylcellulose/citric acid composite or particles thereof arepreferably heated to a temperature of at least about 80° C. tocross-link the carboxymethylcellulose. Any combination of temperatureand time which achieves a desired degree of cross-linking, withoutundesirable damage to the carboxymethylcellulose, is suitable for use inthe present invention. Preferably the composite is heated to atemperature of 80° C. or greater, for example, 100° C. or greater. Incertain embodiments, the temperature is within the range from about 100°C. to about 250° C., preferably from about 100° C. to about 200° C., andmore preferably from about 110° C. to about 150° C. In a particularlypreferred embodiment, the composite is heated to 110 to 130° C. or toabout 120° C. Generally, the heat-treating process will extend over atime period within the range of from about 1 minute to about 600minutes, preferably from about 1 minute to about 300 minutes, and morepreferably from about 175 minutes to about 300 minutes, or about 200 to250 minutes. In preferred embodiments, the composite is crosslinked byheating at about 120° C. for 200 to 250 minutes or about 225 minutes.

The heat treatment of the carboxymethylcellulose/citric acid compositein the methods of the invention causes the carboxymethylcellulose chainsto cross-link via the citric acid and become water-insoluble. Theheat-treating process desirably produces a citric acid crosslinkedcarboxymethylcellulose having an elastic modulus and the ability toabsorb aqueous liquids, in particular stomach fluids which have highsalinity and low pH.

The term “carboxymethylcellulose/citric acid composite” or “composite”as used herein, refers to a substantially dry material comprising amixture of the carboxymethylcellulose and the citric acid. Inembodiments in which this composite is produced by evaporative drying ofthe aqueous solution of high viscosity carboxymethylcellulose and citricacid, the composite is the substantially dry residue which remainsfollowing removal of water. The composite can retain some bound water,and can be, for example, up to 5, 10 or 20% water by weight. Preferablythe composite is about 10% water by weight or less.

Without being bound by theory, it is believed that the preparation ofcrosslinked carboxymethylcellulose as disclosed herein proceeds viacovalent cross-linking of the carboxymethylcellulose with citric acid.FIG. 1 illustrates the cross-linking of a soluble cellulose derivative,such as carboxymethylcellulose, with citric acid. In this mechanism, theC1-carboxyl group of citric acid is activated by anhydride formation atneutral pH and at elevated temperature and in the presence of a verysmall amount of water, and in the absence of catalyst reacts with acellulosic hydroxyl group to form an ester. The C5 carboxyl group isthen activated by anhydride formation and reacts with a hydroxyl groupof another cellulosic polymer chain to form an intermolecular covalentcrosslink, or the same chain to form an intramolecular covalentcrosslink. Because this is an equilibrium reaction with water as aproduct, the more water that is eliminated during the stabilizationprocedure, the higher the degree of conversion that may be achieved.Removal of water from the carboxymethylcellulose/citric acid solution toform a carboxymethylcellulose/citric acid composite before crosslinkingis thus necessary to allow the anhydride formation/esterificationreaction to occur.

The term “carboxymethylcellulose” (CMC), as used herein, refers tocarboxymethylcellulose (cellulose carboxymethyl ether) in the acid form,as a salt or as a combination of the acid form and a salt. Preferredsalt forms include sodium carboxymethylcellulose and potassiumcarboxymethylcellulose. In particularly preferred embodiments, thecarboxymethylcellulose is present in the solution as the sodium salt(NaCMC).

Methods of making carboxymethylcellulose are known to those skilled inthe art. Suitably, a cellulosic material such as cotton or wood pulp isprovided. The cellulosic material may be in the form of fibers or fiberswhich have been comminuted to particulate form. The cellulosic materialis dispersed in an inert solvent such as an alcohol and acarboxyalkylating agent is added to the dispersion. Carboxyalkylatingagents generally comprise a chloroalkanoic acid such as monochloroaceticacid and sodium hydroxide. It is possible to perform thecarboxymethylation of the starting cellulose in such a manner that thesolution of carboxymethylcellulose and water is formed directly. Thatis, the carboxymethylation process may be performed in an aqueous mediumsuch that, upon formation of the carboxymethyl cellulose, it issolubilized in the water. In this manner, no recovery step is necessarybetween formation of the carboxymethylcellulose and the formation of thesolution of carboxymethylcellulose and water.

In certain embodiments, the high-viscosity carboxymethylcellulose isprepared from cellulose from cotton. In other embodiments, thehigh-viscosity carboxymethylcellulose is prepared from cellulose fromboth cotton and wood pulp.

The term “high viscosity carboxymethylcellulose”, as used herein, refersto carboxymethylcellulose, typically as the sodium salt, which forms a1% (wt/wt) solution in water having a viscosity of at least 6000 cps.The viscosity is determined according to the method set forth in Example5 which is in accordance with ASTM D1439-03(2008)e1 (ASTM International,West Conshohocken, Pa. (2008), incorporated herein by reference in itsentirety). In preferred ambodiments, the high viscositycarboxymethylcellulose also has a low polydispersity index, such as apolydispersity index of about 8 or less.

In any embodiment of the invention, the high viscositycarboxymethylcellulose preferably forms a 1% (wt/wt) solution in waterhaving a viscosity at 25° C. of at least about 6000, 7000, 7500, or 8000cps. In certain embodiments, the carboxymethylcellulose forms a 1%(wt/wt) aqueous solution having a viscosity of 6000 to about 10000 cpsor about 6000 to 11000 cps at 25° C. In certain embodiment, thecarboxymethylcellulose forms a 1% (wt/wt) aqueous solution having aviscosity of about 6000 to about 9500 cps or about 7000 to 9500 cps at25° C. In another embodiment, the carboxymethylcellulose forms a 1%(wt/wt) aqueous solution having a viscosity of about 7000 to about 9200cps or about 7500 to 9000 cps at 25° C. In yet another embodiment, thecarboxymethylcellulose forms a 1% (wt/wt) aqueous solution having aviscosity of about 8000 to about 9300 cps, or about 9000 cps at 25° C.Preferably the carboxymethylcellulose is in the form of the sodium salt.In preferred embodiments the carboxymethylcellulose is sodiumcarboxymethylcellulose which forms a 1% (wt/wt) aqueous solution havinga viscosity of about 7800 cps or higher, for example, from about 7800 to11000 cps, or about 8000 cps to about 11000 cps. In preferredembodiments, the high viscosity carboxymethylcellulose further has apolydispersity index (Mw/Mn) of about 8 or less, preferably about 7 orless, or 6 or less. In one embodiment, the polydispersity index is fromabout 3 to about 8, about 3 to about 7, about 3 to about 6.5, about 3.0to about 6; about 3.5 to about 8, about 3.5 to about 7, about 3.5 toabout 6.5, about 3.5 to about 6, about 4 to about 8, about 4 to about 7,about 4 to about 6.5, about 4 to about 6, about 4.5 to about 8, about4.5 to about 7, about 4.5 to about 6.5, about 4.5 to about 6, about 5 toabout 8, about 5 to about 7.5, about 5 to about 7, about 5 to about 6.5,or about 5 to about 6.

As used herein, the term “polydispersity index” in relation to acarboxymethylcellulose refers to the polydispersity index determinedusing the procedure set forth in Example 10.

The high viscosity carboxymethylcellulose or salt thereof preferably hasan average degree of substitution from about 0.3 to about 1.5, morepreferably from about 0.4 to about 1.2.

In particularly preferred embodiments, the high viscositycarboxymethylcelllulose has a degree of substitution from about 0.60 toabout 0.95, 0.65 to 0.95, 0.65 to 0.90, 0.70 to 0.80, 0.72 to 0.78 or0.73 to 0.75. The degree of substitution refers to the average number ofcarboxyl groups present on the anhydroglucose unit of the cellulosicmaterial. Carboxymethylcelluloses having an average degree ofsubstitution within the range of from about 0.3 to about 1.5 aregenerally water-soluble. As used herein, a carboxymethylcellulose isconsidered to be “water-soluble” when it dissolves in water to form atrue solution.

In certain embodiments, the high viscosity carboxymethylcellulose issodium carboxymethylcellulose which forms a 1% (wt/wt) aqueous solutionhaving a viscosity of about 7600 cps or higher, for example, from about7800 to 15000 cps, about 7800 to about 11000 cps, about 8000 to about15000 cps or about 8000 cps to about 11000 cps, and has a polydispersityindex of about 3 to about 8, about 3 to about 7, about 3 to about 6.5,about 3 to about 6; about 3.5 to about 8, about 3.5 to about 7, about3.5 to about 6.5, about 3.5 to about 6, about 4 to about 8, about 4 toabout 7, about 4 to about 6.5, about 4 to about 6, about 4.5 to about 8,about 4.5 to about 7, about 4.5 to about 6.5, about 4.5 to about 6,about 5 to about 8, about 5 to about 7.5, about 5 to about 7, about 5 toabout 6.5, or about 5 to about 6. In certain embodiments, the highviscosity sodium carboxymethylcellulose additionally has a degree ofsubstitution of 0.65 to 0.90, 0.70 to 0.80, 0.72 to 0.78 or 0.73 to0.75.

In particularly preferred embodiments, the high viscosity sodiumcarboxymethylcellulose forms a 1% (wt/wt) aqueous solution having aviscosity at 25° C. of about about 8000 cps to about 11000 cps, has adegree of substitution of 0.65 to 0.90 or 0.70 to 0.80 and apolydispersity of about 4.5 to about 6.5.

In certain embodiments the high viscosity carboxymethylcellulose has aweight average molecular weight (Mw) of at least 2800 kDa whendetermined as described in Example 10. Preferably the Mw is at leastabout 2900 kDa, or at least about 3000 kDa, or from about 2800 kDa toabout 3500 kDa.

The carboxymethylcellulose and the citric acid used in the methods ofthe invention are preferably are each food grade or pharmaceutical gradematerials. For example, carboxymethylcellulose and citric acid are bothused as food additives and pharmaceutical excipients and are, therefore,available in forms which are suitable for these uses.

A suitable carboxymethylcellulose sodium salt for use in the processesof the invention is AQUALON™ 7H4FM sold by Ashland Inc.

The present invention further provides crosslinkedcarboxymethylcelluloses, including superabsorbent crosslinkedcarboxymethylcelluloses, which can be prepared by crosslinking highviscosity carboxymethylcellulose with citric acid, for example, usingthe methods of the invention, also referred to herein as “citric acidcrosslinked carboxymethylcelluloses”. The invention includes articles ofmanufacture, pharmaceutical compositions, foods, foodstuffs and medicaldevices, agriculture and horticulture products, personal hygieneproducts which comprise such crosslinked carboxymethylcelluloses. Theinvention further includes methods of use of the crosslinkedcarboxymethylcelluloses of the invention for the preparation of foods,the treatment of obesity and diabetes and the enhancement of glycemiccontrol.

In certain embodiments, citric acid crosslinked carboxymethylcellulosesproduced by the methods described herein form hydrogels that havegreater elastic modulus than carboxymethylcellulose hydrogels producedusing other methods, while retaining significant absorption properties.In preferred embodiments, the citric acid crosslinkedcarboxymethylcellulose of the invention has a G′ and an MUR as set forthbelow. In more preferred embodiments, the citric acid crosslinkedcarboxymethycellulose additionally has a tapped density as set forthbelow.

The methods of the invention produce citric acid crosslinkedcarboxymethylcelluloses which combine both physical and chemicalcross-linking and which have good mechanical properties, long termstability in dry and swollen form and good retention capacity andbiocompatibility. The crosslinked carboxymethylcelluloses of theinvention exhibit good media uptake properties, high tapped density,high elastic modulus and cost effective production. Further, thecrosslinked carboxymethylcelluloses have rapid media uptake kinetics inbody fluids.

In any embodiment, the citric acid crosslinked carboxymethylcellulosesof the invention preferably have a media uptake ratio in distilled waterof at least about 20, about 30, about 40, about 50, about 60, about 70,about 80, about 90 or about 100. For example, in certain embodiments,the citric acid crosslinked carboxymethylcelluloses of the inventionhave a media uptake ratio in distilled water from about 20 to about1000, from about 35 to about 750, from about 50 to about 500, from about50 to about 250, from about 50 to about 150. In certain embodiments, thecitric acid crosslinked carboxymethylcelluloses of the invention have amedia uptake ratio in distilled water from about 20, 30, 40, 50, 60, 70,80, 90 or 100 to about 120, 150, 200, 300, 400, 500, 600, 700, 800, 900,1000 or greater, or within any range bounded by any one of these lowerlimits and any one of these upper limits.

In certain embodiments, the citric acid crosslinkedcarboxymethylcelluloses of the invention can absorb an amount of one ormore bodily fluids, such as blood, blood plasma, urine, intestinal fluidor gastric fluid, which is at least 10, 20, 30, 40, 50, 60, 70, 80, 90,or 100 times their dry weight. The ability of the citric acidcrosslinked carboxymethylcellulose to absorb bodily fluids can be testedusing conventional means, including testing with samples of bodilyfluids obtained from one or more subjects or with simulated bodilyfluids, such as simulated urine or gastric fluid.

In any embodiment embodiments, the citric acid crosslinkedcarboxymethylcellulose of the invention can preferably absorbsignificant amounts of SGF/water (1:8). In some embodiments, the citricacid crosslinked carboxymethylcelluloses of the invention have a mediauptake ratio of at least 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or 150in SGF/water (1:8). In some embodiments the citric acid crosslinkedcarboxymethylcelluloses of the invention have a media uptake ratio of 10to 300, from 20 to 250, from 30 to 200, from 50 to 180, from 50 to 150,from 50 to 100 or from 50 to 80 in SGF/water (1:8). In preferredembodiments the citric acid crosslinked carboxymethylcellulose has amedia uptake ratio of about 40 or greater or 50 or greater in SGF/water(1:8), for example from about 50 to about 110, about 55 to about 100,about 60 to about 95, about 60 to about 90, about 60 to about 85, about50 to about 120, about 60 to about 100 or about 70 to about 100.

Preferably, the citric acid crosslinked carboxymethylcellulose of theinvention has a G′ when swollen in SGF/water (1:8) of at least 1500 Pa,2000 Pa, 2200 Pa, 2500 Pa, or 2700 Pa as determined according to themethod described in Example 5. In certain embodiments, the citric acidcrosslinked carboxymethylcellulose of the invention has a G′ whenswollen in SGF/water (1:8) of at least about 2800 Pa. In certainembodiments, the citric acid crosslinked carboxymethylcellulose of theinvention has a G′ when swollen in SGF/water (1:8) from about 1800 Pa toabout 4000 Pa, from about 2000 Pa to about 3500 Pa, from about 2100 Pato about 3400 Pa or from about 2500 Pa to about 3500 Pa.

The citric acid crosslinked carboxymethylcelluloses of the invention arepreferably glassy but amorphous or vitreous materials when in asubstantially dry or xerogel form. The citric acid crosslinkedcarboxymethylcellulose of the invention preferably has a tapped densityof at least about 0.45 g/mL. In more preferred embodiments, the tappeddensity is from about 0.50 to about 0.8 g/mL or from about 0.55 to about0.8 g/mL when determined as described in Example 5. In a preferredembodiment, the tapped density is about 0.6 g/mL or greater, forexample, from about 0.6 g/mL to about 0.8 g/mL. In certain embodiments,the tapped density is from about 0.65 g/mL to about 0.75 g/mL.

The citric acid crosslinked carboxymethylcelluloses of the inventioninclude crosslinked polymers having varying extents of hydration. Forexample, the citric acid crosslinked carboxymethylcelluloses can beprovided in a state of hydration ranging from a substantially dry oranhydrous state, such as a xerogel or a state in which from about 0% toabout 5% or up to about 10% of the citric acid crosslinkedcarboxymethylcellulose by weight is water or an aqueous fluid, to statescomprising a substantial amount of water or aqueous fluid, including upto a state in which the citric acid crosslinked carboxymethylcellulosehas absorbed a maximum amount of water or an aqueous fluid. In certainembodiments, the citric acid crosslinked carboxymethylcellulose has awater content of 25% or less, 20% or less, 15% or less, 10% or less or5% or less by weight. Preferably the citric acid crosslinkedcarboxymethylcellulose has a water content of less than about 10% byweight, more preferably about 6% or less or about 5% or less, whendetermined according to the method of Example 5.

In certain embodiments, the invention provides a citric acid crosslinkedcarboxymethylcellulose which, when in the form of particles which are atleast 95% by mass in the range of 100 μm to 1000 μm with an average sizein the range of 400 to 800 μm and a loss on drying of 10% or less(wt/wt), has a G′, media uptake ratio, and tapped density as describedbelow. Such a crosslinked carboxymethylcellulose can be prepared, forexample, according to the methods disclosed herein.

-   -   (A) G′: at least about 1500 Pa, 1800 Pa, 2000 Pa, 2200 Pa, 2500        Pa, or 2700 Pa. In certain embodiments, the crosslinked        carboxymethylcellulose of the invention has a G′ when swollen in        SGF/water (1:8) of at least about 2800 Pa. In certain        embodiments, the crosslinked carboxymethylcellulose of the        invention has a G′ when swollen in SGF/water (1:8) from about        1800 Pa to about 3000 Pa, about 2000 Pa to about 4000 Pa, from        about 2100 Pa to about 3500 Pa, from about 2100 Pa to about 3400        Pa, or from about 2500 Pa to about 3500 Pa.    -   (B) Media uptake ratio (MUR) in SGF/water (1:8): at least about        50, preferably at least about 60. In certain embodiments, the        crosslinked carboxymethylcellulose has an MUR of about 50 to        about 110, about 55 to about 100, about 60 to about 95, about 60        to about 90, or about 60 to about 85.    -   (C) Tapped density: at least 0.5 g/mL, preferably about 0.55        g/mL to about 0.9 g/mL. In a preferred embodiment, the tapped        density is about 0.6 g/mL or greater, for example, from about        0.6 g/mL to about 0.8 g/mL, about 6.5 g/mL to about 7.5 g/mL or        about 0.6 g/mL to about 0.7 g/mL.

In certain embodiments, the invention provides a citric acid crosslinkedcarboxymethylcellulose which has a G′ and media uptake ratio as setforth below when in the form of particles which are at least 95% by massin the range of 100 μm to 1000 μm with an average size in the range of400 to 800 μm and a loss on drying of 10% or less (wt/wt):

-   (A) G′ of about 1200 Pa to about 2000 Pa and a media uptake ratio of    at least about 90;-   (B) G′ of about 1400 Pa to about 2500 Pa and a media uptake ratio of    about 80 to 89;-   (C) G′ of about 1600 Pa to about 3000 Pa and a media uptake ratio of    about 70 to 79;-   (D) G′ of about 1900 Pa to about 3500 Pa and a media uptake ratio of    about 60 to 69;-   (E) G′ of about 2200 Pa to about 4000 Pa and a media uptake ratio of    about 50 to 59; or-   (F) G′ of about 2600 to about 5000 Pa and a media uptake ratio of    about 40 to 49.    In these embodiments, the citric acid crosslinked    carboxymethylcellulose optionally further has a tapped density of at    least 0.5 g/mL, preferably about 0.55 g/mL to about 0.9 g/mL. In a    preferred embodiment, the tapped density is about 0.6 g/mL or    greater, for example, from about 0.6 g/mL to about 0.8 g/mL, about    6.5 g/mL to about 7.5 g/mL or about 0.6 g/mL to about 0.7 g/mL.

In exemplary but non-limiting embodiments, the citric acid crosslinkedcarboxymethylcellulose has a G′ of at least about 2100 Pa and a mediauptake ratio of at least about 80; or a G′ of at least about 2700 Pa anda media uptake ratio of at least about 70.

Unless otherwise noted, all measurements of G′, MUR and tapped densitydescribed herein are made on samples of citric acid crosslinkedcarboxymethylcellulose having (1) a loss on drying of 10% (wt/wt) orless; and (2) are in the form of particulates which are at least 95% bymass in the size range of 100 μm to 1000 μm with an average size in therange of 400 to 800 μm.

The term “simulated gastric fluid/water (1:8)” and the equivalent term“SGF/water (1:8)”, as used herein, refer to a solution preparedaccording to the method described in Example 4.

As used herein, the “media uptake ratio” or “MUR” of a crosslinkedpolymer is a measure of the ability of a crosslinked polymer to absorb aspecified aqueous medium according to the equation:MUR=(W _(swollen) −W _(dry))/W _(dry)where W_(dry) is the weight of the initial dry crosslinked polymersample and W_(swollen) is the weight of the crosslinked polymer atequilibrium swelling. Unless otherwise noted, a reference herein tomedia uptake ratio or MUR refers to the value obtained in SGF/water(1:8) according to the method described in Example 5. It is to beunderstood that the units for MUR values reported herein are g/g.

As used herein, the “elastic modulus” or G′ is determined for acrosslinked polymer swollen in SGF/water (1:8) according to the methoddescribed in Example 5.

As used herein, the “tapped density” of a sample is determined accordingto the method described in Example 5.

As used herein, the “water content” or the “loss on drying” of a sampleis determined according to the method described in Example 5.

The citric acid crosslinked carboxymethylcelluloses of the invention canbe used in methods for treating overweight or obesity, reducing food orcalorie intake, or achieving or maintaining satiety in a subject.Crosslinked carboxymethylcellulose of the invention can also be used toimprove glycemic control and to treat or prevent diabetes in a subject.The methods comprise the step of administering an effective amount of acitric acid crosslinked carboxymethylcellulose of the invention to thestomach of a subject, preferably by oral administration, for example, bycausing the subject, such as a mammal, including a human, to swallow thecitric acid crosslinked carboxymethylcellulose, optionally incombination with ingestion of a volume of water. Upon contacting wateror aqueous stomach contents, the citric acid crosslinkedcarboxymethylcellulose swells and occupies stomach volume decreasing thecapacity of the stomach for food and/or the rate of food absorption.When ingested in combination with food, the citric acid crosslinkedcarboxymethylcellulose increases the volume of the food bolus withoutadding to the calorie content of the food. The citric acid crosslinkedcarboxymethylcellulose can be ingested by the subject prior to eating orin combination with food, for example, as a mixture of the citric acidcrosslinked carboxymethylcellulose with food.

The subject can be, for example, a human subject for whom weight losswill bring health benefits, such as human who is overweight, with a bodymass index of 25 to 29.9, or obese, with a body mass index of 30 orhigher. The subject can also be a human of normal weight, with a bodymass index of 18.5 to 24.9, but at risk of unhealthy weight increase. Ahuman subject can also have one or more other conditions orcomorbidities, such as prediabetes, diabetes or heart disease, inaddition to being overweight or obese. For example, the subject can haveone or more of the following: hypertension, such as blood pressure of140/90 mm Hg or higher; high LDL cholesterol; low HDL cholesterol, forexample less than 35 mg/dL; high triglycerides, for example higher than250 mg/dL; high fasting blood glucose, for example, ≥100 mg/dL; a familyhistory of premature heart disease; physical inactivity; and cigarettesmoking.

In one embodiment, the human subject is prediabetic, as determined byone or more of fasting glucose level, A1C level and oral glucosetolerance test, according to the criteria established by the AmericanDiabetes Association (Diabetes Care 2004, 27:S15-35). For example, aprediabetic subject can have a fasting blood glucose level of 100 mg/dLto 125.9 mg/dL, an A1C level of 5.7 to 6.4% and/or an oral glucosetolerance test result of 140 to 199 mg/dL. Preferably, the prediabeticpatient has a fasting blood glucose level of 100 mg/dL to 125.9 mg/dL.

In another embodiment, the human subject is diabetic, as determined byone or more of fasting glucose level, A1C level and oral glucosetolerance test. For example, a diabetic subject can have a fasting bloodglucose level of 126 mg/dL or higher, an A1C level of 6.5% or higherand/or an oral glucose tolerance test result of 200 mg/dL or higher.Preferably, the diabetic patient has a fasting blood glucose level of126 mg/dL or higher.

In another embodiment, the subject has metabolic syndrome, as diagnosedusing the criteria set forth by the American Heart Association in 2004(Grundy S M, et al., Circulation, 2004; 109:433-438). According to theseguidelines, a subject is diagnosed with metabolic syndrome if at leastthree of the following five conditions are present: (1) elevated waistcircumference (men: >40 inches; women: >35 inches); (2) elevatedtriglycerides (150 mg/dL or higher); (3) reduced HDL cholesterol (men:less than 40 mg/dL; women: less than 50 mg/dL); (4) elevated bloodpressure (130/85 mm Hg or higher) or use of medication for hypertension;(5) elevated fasting glucose (≥100 mg/dL) or use of medication forhyperglycemia.

In another embodiment, the subject has a fasting glucose level of about90 mg/dL or higher or about 92 or 93 mg/dL or higher. Subjects withfasting glucose levels in this range include those with normal fastingglucose levels (90 to under 100 mg/dL), prediabetes (100-125 mg/dL) anddiabetes (126 mg/dL or higher).

The citric acid crosslinked carboxymethylcellulose is preferablyadministered in combination with water. The amount of water administeredis preferably an amount effective to swell the citric acid crosslinkedcarboxymethylcellulose in the stomach of the subject. In one embodiment,at least about 100 mL of water per gram of crosslinkedcarboxymethylcellulose is administered. The water can be administeredconcomitant with or following administration of the pharmaceuticalcomposition.

In one embodiment, the citric acid crosslinked carboxymethylcellulose isadministered prior to or with a meal, for example, up to 2 hours, 1 houror 0.5 hour prior to the meal.

The citric acid crosslinked carboxymethylcellulose can be ingestedalone, in a mixture with liquid or dry food or as a component of a foodor edible matrix, in a dry, partially swollen or fully swollen state,but is preferably ingested in a state of hydration which issignificantly below its fluid capacity, more preferably the citric acidcrosslinked carboxymethylcellulose is ingested in a substantiallyanhydrous state, that is, about 10% or less water by weight. The citricacid crosslinked carboxymethylcellulose can be formulated for oraladministration in a capsule, sachet or tablet or suspension. Whenadministered in a substantially anhydrous form, the volume of thestomach taken up by the citric acid crosslinked carboxymethylcellulosewill be significantly greater than the volume of the citric acidcrosslinked carboxymethylcellulose ingested by the subject. The citricacid crosslinked carboxymethylcelluloses of the invention can also takeup volume and/or exert pressure on the wall of the small intestine bymoving from the stomach into the small intestine and media uptake.Preferably, the citric acid crosslinked carboxymethylcellulose willremain swollen in the small intestine for a period of time sufficient toinhibit the intake of food by the subject, before shrinking sufficientlyfor excretion from the body. The time sufficient to inhibit the intakeof food by the subject will generally be the time required for thesubject to eat and for the ingested food to pass through the smallintestine; Such shrinking can occur, for example, by degradation throughloss of cross-links, releasing fluid and decreasing in volumesufficiently for excretion from the body.

The data presented in Example 6 show that hydrogels prepared asdescribed herein provide a greater barrier to the diffusion of glucosecompared to hydrogels prepared with a lower viscositycarboxymethylcellulose. In addition, Example 9 shows that swollencrosslinked carboxymethylcelluloses prepared as described herein haverheological properties similar to those of masticated food. Followingoral administration, these materials therefore are expected to mimicfood as they pass through the digestive tract. For example, thesematerials may mimic the undigested food to which the intestine isexposed following gastric bypass, which is thought to play a role inregulation of glucose in bypass patients (Saeidi N. et al., Science2013, 341(6144):406-10). Thus, the crosslinked carboxymethylcellulose ofthe invention may enhance glycemic control through multiple mechanisms.

The citric acid crosslinked carboxymethylcelluloses of the inventionexhibit pH-dependent media uptake due to the presence of ionic groupsattached to the polymer backbone, with greater media uptake observed athigher pH than at lower pH. Thus, such a polymer will not swellsignificantly in the stomach unless food and/or water is present toraise the pH of the stomach contents and will move into the smallintestine. When ingested with food, the citric acid crosslinkedcarboxymethylcellulose preferably swells initially in the stomach,shrinks when the stomach is emptied of food and the pH drops and thenmoves from the stomach to the small intestine. In the higher pHenvironment of the small intestine the citric acid crosslinkedcarboxymethylcellulose will swell again, taking up volume in the smallintestine and/or exerting pressure on the wall of the small intestine.

The citric acid crosslinked carboxymethylcellulose can optionally beadministered in combination with a pH modifying agent, which is an agentwhich alters the pH of the microenvironment of the citric acidcrosslinked carboxymethylcellulose, thereby modifying its ability toabsorb fluids. For example, for citric acid crosslinkedcarboxymethylcelluloses comprising an anionic polymer, agents whichincrease the pH of the microenvironment can increase the swellability ofthe citric acid crosslinked carboxymethylcellulose. Suitable pHmodifying agents for use with the citric acid crosslinkedcarboxymethylcelluloses of the invention include buffering agents, H₂blockers, proton pump inhibitors, antacids, proteins, nutritionalshakes, and combinations thereof. Suitable buffering agents and antacidsinclude ammonium bicarbonate, sodium bicarbonate, calcium carbonate,calcium hydroxide, aluminium hydroxide, aluminium carbonate, magnesiumcarbonate, magnesium hydroxide, potassium bicarbonate, potassiumcarbonate, potassium hydroxide, sodium carbonate, sodium hydroxide andcombinations thereof. Suitable H₂ blockers include cimetidine,ranitidine, famotidine, nizatidine and combinations thereof. Suitableproton pump inhibitors include omeprazole, lansoprazole, esomeprazole,pantoprazole, abeprazole, and combinations thereof.

The citric acid crosslinked carboxymethylcellulose of the invention canbe administered to the subject in the form of a tablet, a capsule asachet or other formulation suitable for oral administration. The tabletor capsule can further include one or more additional agents, such as apH modifying agent, and/or a pharmaceutically acceptable carrier orexcipient. The citric acid crosslinked carboxymethylcellulose can alsobe administered as a component of a food or a beverage, such as isdescribed in WO 2010/059725, incorporated herein by reference in itsentirety.

In one embodiment, the present invention provides a pharmaceuticalcomposition comprising a citric acid crosslinked carboxymethylcelluloseof the invention. The pharmaceutical composition can comprise the citricacid crosslinked carboxymethylcellulose as an active agent, optionallyin combination with a pharmaceutically acceptable excipient or carrier.For example, the pharmaceutical composition can be intended for oraladministration to treat obesity, provide enhanced satiety, improveglycemic control, treat or prevent diabetes or aid in weight management.

In another embodiment, the pharmaceutical composition comprises thecitric acid crosslinked carboxymethylcellulose in combination withanother active agent.

In one embodiment, the invention provides a pharmaceutical compositioncomprising a citric acid crosslinked carboxymethylcellulose of theinvention having (1) a loss on drying of 10% (wt/wt) or less; and (2)are in the form of particulates which are at least 95% by mass in thesize range of 100 μm to 1000 μm with an average size in the range of 400to 800 μm. The citric acid crosslinked carboxymethylcellulose can be,for example, encapsulated in a capsule, such as a hard or soft gelatincapsule. Preferably, the composition does not comprise a disintegrant.In certain embodiments, the capsule is a hard gelatin capsule size 00EL,and under the conditions described in Example 7 (37° C. in SGF/water1:8), the capsule disintegrates within 7.5 minutes and the citric acidcrosslinked carboxymethylcellulose is homogeneously hydrated within 15minutes.

The scope of the present invention includes the use of the citric acidcrosslinked carboxymethylcelluloses of the invention as an absorbentmaterial in products which are capable of absorbing water and/or aqueoussolutions and/or which are capable of media uptake when brought intocontact with water and/or an aqueous solution. The citric acidcrosslinked carboxymethylcellulose of the present invention may be usedas an absorbent material in the following fields, which are provided asnon-limiting examples: dietary supplements (for example, as the bulkingagents in dietary supplements for hypocaloric diets capable ofconferring a sensation of lasting satiety being retained into thestomach for a limited period of time, or as water and low molecularweight compounds supplements, such as mineral salts or vitamins, to beincluded into drinks in a dry or swollen form); in agriculturalproducts, for example, in devices for the controlled release of waterand/or nutrients and/or phytochemicals, particularly for cultivation inarid, deserted areas and in all cases where it is not possible to carryout frequent irrigation; such products, mixed in a dry form with thesoil in the areas surrounding the plant roots, absorb water duringirrigation and are capable of retaining it, releasing it slowly incertain cases, together with the nutrients and phytochemicals useful forcultivation; in personal hygiene and household absorbent products, suchas, for example, as the absorbent core in diapers, sanitary napkins andthe like; in toys and devices, such as for example in products which arecapable of significantly changing their size once brought into contactwith water or an aqueous solution; in the biomedical field, for example,in biomedical and/or medical devices such as absorbent dressings for thetreatment of highly exudative wounds, such as ulcers and/or burns, or inslow-release polymeric films suitable to slowly release liquids adaptedfor use in ophthalmology; in the body fluid management field, forexample, for controlling the amount of liquids in an organism, forexample in products capable of promoting the elimination of fluids fromthe body, such as, for example, in the case of edema, CHF (congestiveheart failure), dialysis; and in home cleaning products.

The above-mentioned products, containing a citric acid crosslinkedcarboxymethylcellulose of the present invention as the absorbentmaterial, also fall within the scope of the invention.

The invention further includes the use of any of the citric acidcrosslinked carboxymethylcelluloses of the invention in medicine. Suchuse includes the use of a crosslinked carboxymethylcellulose in thepreparation of a medicament for the treatment of obesity or any medicaldisorder or disease in which calorie restriction has a therapeutic,palliative or prophylactic benefit.

The citric acid crosslinked carboxymethylcelluloses of the inventionhave advantages over previously described crosslinkedcarboxymethylcellulose, such as those exemplified in US 2013/0089737. Asset forth in the examples, citric acid crosslinkedcarboxymethylcelluloses produced using high viscositycarboxymethylcellulose have comparable media uptake ratio and tappeddensity compared to those produced with lower viscositycarboxymethylcellulose while having a significantly higher G′. Asdemonstrated in the examples, the citric acid crosslinkedcarboxymethylcellulose of the invention provides a stronger barrier toglucose diffusion, faster and more homogeneous swelling and consistentcapsule opening without the need for a disintegrant compared to citricacid crosslinked carboxymethylcellulose produced with lower viscositycarboxymethylcellulose. The citric acid crosslinkedcarboxymethylcellulose of the invention is also sensitive to changes inpH of the external environment. Oral dosage forms including the citricacid crosslinked carboxymethylcellulose would therefore be expected toresult in slower gastric emptying, enhanced glycemic control, moreconsistent dosing and more rapid onset of action compared to prior artcrosslinked carboxymethylcellulose. The improved elasticity of thesematerials may also play a fundamental role in activating metabolicpathways in the lower GI tract for improved weight loss (Saeidi N, etal., Science 2013, 341(6144):406-10).

EXAMPLES Example 1 Preparation of CrosslinkedCarboxymethylcellulose-Laboratory Scale

Crosslinked carboxymethylcellulose was produced using the followingprotocol.

Materials

-   Carboxymethylcellulose sodium salt (CMCNa): Aqualon 7H4FM (Ashland    Inc.), viscosity range 7600-9000 cps (1% wt/wt solution in water at    25° C.)-   Citric acid-   Purified water

Purified water (3 kg) was placed to a mixing bowl. 0.36 g citric acidwas added and the mixture was stirred until the citric acid wascompletely dissolved. 180 g CMCNa was slowly added to the citric acidsolution and the resulting suspension was mixed continuously for 18hours using a mixer with a flat blade.

A portion of the material from the mixing bowl was placed with a spoonon a silicone sheet on a stainless steel tray. Using a plastic spatulathe material was spread until it appeared uniform without spilling overthe edges. This was repeated using additional trays until all of thematerial was spread on trays.

The trays in an oven set to 50° C. When drying was complete (about 23hours) the trays were removed from the oven. In this and the otherexamples set forth herein, drying is considered complete when the losson drying, determined as described in Example 5, is 10% or less.

The sheets of dried material remaining after drying were broken intosmaller pieces that could be easily ground. The grinding was started byinserting the material slowly into a collection bin to insure that thematerial did not overheat on grinding. At the end of the grinding, thematerial was sieved between 100 and 1600 μm.

The ground material (50 g) was placed in a small aluminum dish. Thealuminum dish was placed in an oven heated to 120 (±1)° C. to inducecrosslinking. The dish was removed from the oven after 4 hours.

The crosslinked material (10 g) was placed in a beaker with 1500 g waterand stirred at room temperature for 3 hours. The resulting swollenmaterial was filtered and the water was removed using a vacuum pump. Theratio of swelling obtained was 55.6 g/g.

The washed material was placed on a plastic tray. Using a plasticspatula, the material was spread evenly in the trays. The trays wereplaced in an oven set to 50 (±1)° C. After drying was complete (20 h),the trays were removed from the oven.

The dried material was inserted slowly into the collection bin of agrinder to insure that it would not overheat on grinding. The groundmaterial was sieved between 100 and 1000 μm.

The media uptake ratio of the resulting powder, determined as set forthin Example 5, was 73. The G′ was determined as described in Example 5and was 2028 Pa.

Example 2 Preparation of Crosslinked Carboxymethylcellulose-Large Scale

Crosslinked carboxymethylcellulose was produced on a large scale usingthe following protocol.

Materials

-   Carboxymethylcellulose sodium salt (CMCNa): AQUALON™ 7H4 FM (Ashland    Inc.), viscosity range 7600-9000 cps (1% wt/wt solution in water at    25° C.)-   Citric acid-   Purified water

To 5 kg of CMCNa in a mixing bowl was added 21 kg of water and mixingwas begun. After 10 minutes a solution of 5 g citric acid in 21 kg ofwater was under constant mixing for 10 minutes. 21 kg of water was thenadded and mixed for 10 minutes. Finally, a solution of 5 g citric acidin 21 kg of water was add and the mixture was mixed for 200 minutes.

A portion of the material from the mixing bowl was placed with a spoonon a silicone sheet on a stainless steel tray. Using a plastic spatulathe material was spread until it appeared uniform without spilling overthe edges. This was repeated using additional trays until all of thematerial was spread on trays.

The trays were placed in an oven set to 70° C. When drying was complete(48 hours) the trays were removed from the oven.

The sheets of dried material were broken into smaller pieces that couldbe easily ground. The grinding was started by inserting the materialslowly into a collection bin to insure that the material did notoverheat on grinding. At the end of the grinding, the material wassieved between 100 and 1600 μm.

The ground material was placed in a stainless steel drum. The drum wasplaced in an oven heated to 120 (±1)° C. to induce crosslinking. Thedrum was removed from the oven after 4 hours.

1 kg of the crosslinked material was placed in a stainless steel tankwith 150 kg water with constant stirring at room temperature for 4hours. The resulting swollen material was filtered using a sieve and thewater was removed using a vacuum pump. The ratio of swelling obtainedwas 73.2 g/g.

The washed material was placed on plastic trays. Using a plasticspatula, the material was spread evenly in the trays. The trays wereplaced in an oven set to 70 (±1)° C. After drying was complete (72 h),the trays were removed from the oven.

The dried material was inserted slowly into the collection bin of agrinder to insure that it would not overheat on grinding. The groundmaterial was sieved between 100 and 1000 μm.

The media uptake ratio of the resulting powder, determined as set forthin Example 5, was 70.29 g/g. The G′ determined as described in Example 5was 2967 Pa.

Citric acid crosslinked carboxymethylcellulose was also prepared usingthe general method above, but with a total of 15.0 g citric acid. Thematerials resulting from these syntheses were characterized as providedin Tables 1 and 2 below. In each case, a portion of thecarboxymethylcellulose/citric acid composite was crosslinked.

TABLE 1 Viscosity of CMC (cps, 1% LOD Weight Weight aqueous Weight afterbefore Washing before after solution at 1st sieving crosslink Crosslinkratio Washing Washing Run 25° C.) [g] (100-1600 μm) (wt %) time [h][kg/L] [g] [kg] 1 9000 4717.8 3.40 4 1/150 1079.8 87.00 2 9000 4756.53.96 4.5 1/150 1070.0 65.00 3 8900 4775.4 4.47 4 1/150 1084.0 96.60 48900 4755.7 3.68 4.5 1/150 1270.0 90.30 5 7600 4878.2 6.38 4 1/1502186.0 202.00 6 7600 4874.0 5.37 4.5 1/150 2190.0 182.90

TABLE 2 Weight after Tapped Swelling 2nd sieving Yield LOD density Runin washing [g] (100-1000 μm) [%] MUR G′ [Pa] (wt %) [g/mL] 1 79.6 791.763.34% 87.50 2025 4.07 0.7 2 59.7 893.2 71.46% 61.66 3252 9.86 0.7 388.1 733.3 58.66% 80.28 2749 3.18 0.6 4 70.1 1037.3 69.85% 56.81 33967.82 0.7 5 91.4 1233.0 49.32% 82.01 2195 3.74 0.6 6 82.5 1673.2 66.93%66.47 2570 11.17 0.6

Example 3 Preparation of Crosslinked Carboxymethylcellulose with LowerViscosity Carboxymethylcellulose

Purified water (80 kg) was added to a 140 liter Hobart mixer andagitated. Citric acid (14.4 g) was added to the water and dissolved.CMCNa (4.8 kg; 7H3SXF (AQUALON™)), having a viscosity of 1000-2600 cpsas a 1% (wt/wt) solution in water at 25° C., was then added to thesolution and the resulting mixture was agitated at room temperature for4 hours. The resulting solution was added to 30 stainless steel trays(2700 g solution per tray). The trays were placed in a SHELLAB oven at70° C. for 48 hours. After the desiccation the material was ground bymeans of a cutting mill (Retsch cutting mill) equipped with a 2 mmscreen. The granulated material was then sieved between 0.1-1.6 mm andthen placed into the stainless-steel drum for the cross-linking reactionin the Salvis Thermocenter TC240 oven at 120° C. for 7 hours. Thecrosslinked polymer hydrogel thus obtained was washed with purifiedwater for 3 hours under mild agitation to remove the unreacted reagents.The washing stage allows the media uptake of the crosslinked polymer byincreasing the relaxation of the network thus increasing the mediauptake capacity of the final material obtained after a furtherdesiccation step. After the washing the material was placed on trays andplaced in the oven at 70° C. for 72 h to dry. The dry material was thenground and sieved to a particle size from 100 μm to 1000 μm.

Example 4 Preparation of Simulated Gastric Fluid/Water (1:8)

Reagents used for preparation of SGF/water (1:8) solution are purifiedwater, sodium chloride, 1M hydrochloric acid and pepsin.

-   1. To a 1 L graduated cylinder pour about 880 mL of water.-   2. Place the cylinder on a magnetic stirrer, add a magnetic bar and    start stirring.-   3. Begin monitoring the pH of the water with a pH meter.-   4. Add a sufficient amount of 1M hydrochloric acid to bring the pH    to 2.1±0.1.-   5. Add 0.2 g NaCl and 0.32 g pepsin. Leave the solution to stir    until complete dissolution.-   6. Remove the magnetic bar and the electrode from the cylinder.-   7. Add the amount of water required to bring the volume to 900 mL.

Example 5 Characterization of Carboxymethylcellulose and CrosslinkedCarboxymethylcellulose

(A) Determination of Viscosity of Carboxymethylcellulose Solutions

-   Equipment and Materials:-   Constant temperature water bath.-   Glass Bottle, 500 ml with a cap, diameter of the neck at least 80    mm.-   Brookfield Viscometer, model Myr VR3000 (ECO208) or equivalent    equipped with:-   Spindle L4-   Thermal printer (PRP-058GI)-   Mechanical overhead stirrer with anchor stainless steel stirrer.-   Chain clamp to secure glassware.-   Lab spatula.-   Aluminum crucible-   Analytical balance, capable of weighing to the nearest 0.001 g.-   Calibrated balance, capable of weighing, to the nearest 0.1 g.-   Purified water    Procedure    Preparation of Test Samples:-   Prepare three CMC/water solutions as described below:-   1. Measure the moisture content of CMC powder as described in [B]    below.-   2. Calculate the amount of water required using the equation:    water required [g]=3*(99−LOD_(average)).-   3. Weigh the needed amount of water for preparing the CMC solution    into a beaker.-   4. Pour roughly half of this water into the bottle, with the rest of    the water remaining in the beaker.-   5. Place and tie up the bottle under the stirrer motor with a chain    clamp.-   6. Insert the stirrer.-   7. Mix the sample to assure uniformity.-   8. Weigh 3.0±0.1 g of CMC powder.-   9. Pour the powder in small amounts into the bottle while mixing at    low speed (ca. 600 rpm).-   10. Mix for 2 minutes and set the mixing speed to 1000 rpm.-   11. Mix for no less than 10 minutes but no more than 30 minutes.-   12. Add the remaining water.-   13. Mix for additional 30 minutes.-   14. If the CMC is not dissolved completely, continue stirring.-   15. Once all the CMC is dissolved remove the anchor stainless steel    stirrer and place the cap on the bottle.-   16. Place the flask in the constant temperature bath, at 25.0°    C.±0.1° C., for at least 30 minutes but no longer than one hour.-   17. Shake the bottle vigorously for 10 seconds. The solution is    ready to be tested.    Viscosity Measurement:-   1. Determine viscosity of each sample according to the instructions    for the viscometer. Allow rotation of spindle for exactly 3 minutes.-   2. Determine the average viscosity of the three solutions.

(B) Determination of Loss on Drying

The moisture content of a carboxymethylcellulose or crosslinkedcarboxymethylcellulose is determined according to USP <731>, Loss onDrying.

Instruments/Equipment

-   Moisture Analyzer Radwag, Model WPS 505-   Lab Spatula-   Aluminum crucible-   Desiccator with silica gel    Procedure-   1. Place the sample in the desiccator for at least 12 hours.-   2. Place the aluminum crucible on the scale pan of the moisture    analyzer and tare the balance.-   3. Accurately weigh 1.000±0.005 g of a sample in the aluminum    crucible. The initial weight of the sample is W_(i).-   4. Set the Moisture Analyzer to heat the sample at 105° C. for 30    minutes under ambient pressure and moisture.-   5. Turn on the Moisture Analyzer and run the LOD program (30 min at    105° C.).-   6. Weigh the sample. The final weight of the sample is W_(f).-   The LOD value is determined according to the equation:    LOD=(W _(i) −W _(f))/W _(i)×100%.    The Loss on Drying is determined in triplicate, and the reported LOD    is the average of the three values.

(C) Determination of Particle Size Range

Equipment and Materials:

-   Sieve Shaker Retsch, Model AS 200 basic-   Stainless Steel Sieves with mesh sizes 1000 μm and 100 μm-   Aluminum weighing pan-   Laboratory stainless steel spatula-   Calibrated balance, capable of weighing to the nearest 0.1 g.    Procedure:-   1. Weigh the empty sieves and the aluminum pan to the nearest 0.1 g.-   2. Weigh out 40.0±0.1 g of powder.-   3. Stack the test sieves with sizes 1000 and 100 μm with larger pore    size on the top and the smaller at the bottom. Assemble the aluminum    pan at the bottom of the nest.-   4. Pour the sample into the 1000 μm sieve, at the top of the stack.-   5. Place this stack between the cover and the end pan of the shaker,    so that the sample remains in the assembly.-   6. Turn on the main switch of the shaker.-   7. Set knob UV2 of the shaker for continuous operation.-   8. Turn the knob MN2 of the shaker to the right to increase the    vibration height until 50.-   9. Shake this stack with the shaker for 5 minutes.-   10. Disassemble the sieve and reweigh each sieve.-   11. Determine the percentage weight of test specimen in each sieve    as described in paragraph 8.-   12. After measuring the weight of the full and empty test sieves,    determine, by difference, the weight of the material inside each    sieve.-   13. Determine the weight of material in the collecting pan in a    similar manner.-   14. Use the weight of sample contained in each sieve and in the    collecting pan to calculate the % distribution with the following    equation:    Wx%=Wx/Wsample*100%    where:-   Wx %=sample weight in each sieve or in the collecting pan, in    percentage where the index “x” is:-   “>1000” for particle size bigger than 1000 μm.-   “100-1000” for particle size between 100 and 1000 μm.-   “<100” for particle size smaller than 100 μm.-   Wsample=initial weight of test specimen.

(D) Determination of Tapped Density

Equipment and materials:

-   100 mL glass graduated cylinder-   100 mL glass beaker-   Lab spatula-   Mechanical tapped density tester, Model JV 1000 by Copley Scientific-   Calibrated balance capable of weighing to the nearest 0.1 g.    Procedure:-   1. Weigh out 40.0±0.1 grams of test sample. This value is designated    M.-   2. Introduce the sample into a dry 100 mL glass graduated cylinder.-   3. Carefully level the powder without compacting and read the    unsettled apparent volume, V0, to the nearest graduated unit.-   4. Set the mechanical tapped density tester to tap the cylinder 500    times initially and measure the tapped volume, V500, to the nearest    graduated unit.-   5. Repeat the tapping 750 times and measure the tapped volume, V750,    to the nearest graduated unit.-   6. If the difference between the two volumes is less than 2%, V750    is the final tapped volume, Vf, otherwise repeat in increments of    1250 taps, as needed, until the difference between succeeding    measurements is less than 2%.    Calculations:-   Calculate the Tapped Density, DT, in gram per mL, by the formula:    DT=M/Vf    where:-   M=Weight of sample, in grams, rounded off to the nearest 0.1 g.-   Vf=Final volume, in mL.

(E) Determination of Media Uptake Ratio in SGF/Water (1:8)

The media uptake ratio of a crosslinked carboxymethylcellulose inSGF/water (1:8) is determined according to the following protocol.

-   1. Place a dried fitted glass funnel on a support and pour 40.0±1.0    g of purified water into the funnel.-   2. Wait until no droplets are detected in the neck of the funnel    (about 5 minutes) and dry the tip of the funnel with an absorbent    paper.-   3. Place the funnel into an empty and dry glass beaker (beaker #1),    place them on a tared scale and record the weight of the empty    apparatus (W_(tare)).-   4. Put a magnetic stir bar in a 100 mL beaker (beaker #2); place    beaker #2 on the scale and tare.-   5. Add 40.0±1.0 g of SGF/Water (1:8) solution prepared as described    above to beaker #2.-   6. Place beaker #2 on the magnetic stirrer and stir gently at room    temperature.-   7. Accurately weigh 0.250±0.005 g of crosslinked    carboxymethylcellulose powder using a weighing paper (W_(in)).-   8. Add the powder to beaker #2 and stir gently for 30±2 min with the    magnetic stirrer without generating vortices.-   9. Remove the stir bar from the resulting suspension, place the    funnel on a support and pour the suspension into the funnel,    collecting any remaining material with a spatula.-   10. Allow the material to drain for 10±1 min.-   11. Place the funnel containing the drained material inside beaker    #1 and weigh it (W′_(fin)).-   The Media Uptake Ratio (MUR) is calculated according to:    MUR=(W _(fin) −W _(in))/W _(in).    W_(fin) is the weight of the swollen hydrogel calculated as follows:    W _(fin) =W′ _(fin) −W _(tare).    W_(in) is the weight of the initial dry sample.

The MUR is determined in triplicate for each sample of crosslinkedcarboxymethylcellulose and the reported MUR is the average of the threedeterminations.

(F) Determination of Elastic Modulus

The elastic modulus (G′) is determined according to the protocol setforth below. The rheometer used is a Rheometer Discovery HR-1 (5332-0277DHR-1) by TA Instruments or equivalent, equipped with a Peltier Plate; aLower Flat plate Xhatch, 40 mm diameter; and an Upper Flat plate Xhatch,40 mm diameter.

-   1. Put a magnetic stir bar in a 100 mL beaker.-   2. Add 40.0±1.0 g of SGF/Water (1:8) solution prepared as described    above to the beaker.-   3. Place the beaker on the magnetic stirrer and stir gently at room    temperature.-   4. Accurately weigh 0.250±0.005 g of crosslinked    carboxymethylcellulose powder using a weighing paper (W_(in)).-   5. Add the powder to the beaker and stir gently for 30±2 min with    the magnetic stirrer without generating vortices.-   6. Remove the stir bar from the resulting suspension, place the    funnel on a support and pour the suspension into the funnel,    collecting any remaining material with a spatula.-   7. Allow the material to drain for 10±1 min.-   8. Collect the resulting material.-   9. Subject the material to a sweep frequency test with the rheometer    and determine the value at an angular frequency of 10 rad/s.

The determination is made in triplicate. The reported G′ value is theaverage of the three determinations.

(G) Comparison of Properties of Crosslinked CarboxymethylcellulosePrepared with High Viscosity and Lower Viscosity Carboxymethylcellulose

The table below shows the ranges of MUR, G′ and tapped density obtainedfor multiple samples of citric acid crosslinked carboxymethylcelluloseprepared by the methods described in Examples 2 (High Viscosity) and 3(Lower Viscosity). The measurements described below were made usingsamples of crosslinked carboxymethylcellulose with the followingcharacteristics 1) a loss on drying of 10% or less; and (2) in the formof particulates which are at least 95% by mass in the size range of 100μm to 1000 μm with an average size in the range of 400 to 800 μm.

TABLE 3 Lower Viscosity High Viscosity MUR (g/g)  75-108 60-85 G′ (Pa)1600-590  3400-2100 Tapped density 0.7-0.8 0.6-0.7 (g/cm³)The results show that the materials prepared from high viscositycarboxymethylcellulose have MUR values and tapped densities comparableto the materials prepared from lower viscosity carboxymethylcellulose.Notably, the materials prepared from high viscositycarboxymethylcellulose have a significantly higher G′ than the materialsprepared from lower viscosity carboxymethylcellulose.

Example 6 Inhibition of Glucose Diffusion

Hydrogel A was Prepared as Described in Example 3.

Hydrogel B

Hydrogel B was prepared as described below. This method is substantiallysimilar to the method described in Example 2.

Purified water (80 kg) was added to a 140 L Hobart mixer and agitated.Citric acid (9.6 g) was added to the water and dissolved. CMCNa (Aqualon7H4 FM (Ashland Inc.), viscosity range 6000-9000; 4.8 kg) was then addedto the solution and the resulting mixture was agitated at roomtemperature for 4 hours. The resulting solution was added to 30stainless steel trays (2,700 g solution per tray). The trays were placedin a SHELLAB oven at 70° C. for 48 hours. After the desiccation thematerial was ground by means of a cutting mill (Retsch cutting mill)equipped with a 2 mm screen. The granulated material was then sievedbetween 0.1-1.6 mm and then placed into the stainless-steel drum for thecross-linking reaction in the Salvis Thermocenter TC240 oven at 120° C.for 4 hours. The crosslinked polymer hydrogel thus obtained was washedwith purified water for 3 hours under mild agitation to remove theunreacted reagents. The washing stage allows the media uptake of thecrosslinked polymer by increasing the relaxation of the network thusincreasing the media uptake capacity of the final material obtainedafter a further desiccation step. After the washing the material wasplaced on trays and placed in the oven at 70° C. for 72 h to dry. Thedry material was then ground and sieved to a particle size from 100 μmto 1000 μm.

The ability of glucose to diffuse through swollen crosslinkedcarboxymethycellulose was determined using the following procedure:

-   1. Solubilize glucose in water overnight at a concentration of 1000    mg/dL.-   2. Prepare the dialysis tube washing it in a beaker with purified    water for 3 hours, and replacing the water every hour.-   3. Put 0.5% (w/V) dry crosslinked carboxymethylcellulose in 80 mL of    glucose solution and stir for 30 minutes.-   4. Pour the hydrated gel and the glucose solution from step 3 into    the open end of the dialysis tube and seal with two dialysis tubing    closures.-   5. Place the dialysis tube in the plastic bag containing purified    water at 37° C.-   6. Measure the glucose concentration of the dialysate at 15 minutes,    30 minutes and every 30 minutes to 300 minutes using an Accu-Chek™    glucometer.    Results

Hydrogel A was produced according to the method of Example 3, above,which is substantially as described in Example 7 of US PublishedApplication 2013/0089737, incorporated herein by reference in itsentirety, starting with AQUALON™ 7H3 SXF carboxymethylcellulose sodium(Ashland Inc.), which has a viscosity of 1,000 to 2,800 cps as a 1%(wt/wt) solution in water at 25° C. Hydrogel B was produced as describedabove, starting with AQUALON™ 7H4FM carboxymethylcellulose sodium(Ashland Inc.), having a viscosity of 6000 to 9000 cps as a 1% (wt/wt)solution in water at 25° C.

FIG. 2 is a graph showing the dialysate glucose concentration forHydrogel A and Hydrogel B as a function of time. The results show thatglucose diffuses across the dialysis membrane significantly more rapidlyfor Hydrogel A than for Hydrogel B. This suggests that Hydrogel B wouldbe more effective than Hydrogel A at inhibiting glucose diffusion to theintestinal wall in vivo, and thus, more effective at slowing the rate ofglucose absorption.

Example 7 Opening of Crosslinked Carboxymethylcellulose Filled Capsules

The disintegration of hard size 00EL gelatin capsules filled withcrosslinked carboxymethylcellulose was determined according to theprocedure described in USP <701>, incorporated herein by reference inits entirety.

Apparatus

-   pH meter, Model PC 700 by Eutech Instrument or equivalent-   Analytical balance, capable of weighing, to the nearest 0.01 g-   Weighing paper-   Lab spatula-   1 L graduated cylinder-   Magnetic stirrer    Disintegration tester, model DTG 1000 by Copley Scientific    (Equipment Code: EC0067), which is equipped with:-   A one piece PETG water bath-   External thermo-stirrer heater with over-temperature/low water-level    safety cut-offs-   Temperature measurement by Pt100 probe-   A 1000 mL-Beaker-   Basket rack assembly-   1. Place SGF/Water (1:8) solution prepared as in Example 3 in the    1000 mL beaker. The volume of the fluid in the vessel is such that    at the highest point of the upward stroke the wire mesh remains at    least 15 mm below the surface of the fluid and descends to not less    than 25 mm from the bottom of the vessel on the downward stroke. At    no time should the top of the basket-rack assembly become submerged.-   2. Turn on the heater on the disintegration bath and set the    temperature to 37° C.-   3. To perform the test, ensure that the water bath temperature is    37° C.±2° C., that the temperature of the media in the test vessel    is correct and that the disintegration basket to contain the dosage    units under test is mounted on the hanger bar.-   4. Drop one capsule into each of the 6 capsule compartments in the    baskets.-   5. Set the disintegration tester to run for 7.5 min.-   6. At the end of the set time the basket will be lifted from the    vessel. Examine the status of capsules and determine how many have    disintegrated. If some capsules have not disintegrated, the tester    can be run for an additional 7.5 min. and the extent of    disintegration determined again.

The Capsules Disintegration Test was performed according to USP <701> onHydrogels A and B as described in Example 6. The test is designed toquantify the correct disintegration of capsules in simulated gastricmedia (SGF/water 1:8). The test was run for 15 min with an intermediatecheck timepoint at 7.5 min. The operator considered the capsule to becompletely disintegrated only if there was an absence of pieces of thestarting capsule in the basket. The operator also collected informationregarding the presence of aggregates or lumps at the end of the test bypouring the material onto a stainless tray.

For both Hydrogels A (including fumarate as disintegrant) and B (withoutdisintegrant), the gelatin capsules were disintegrated after 7.5minutes, but the samples showed different hydration. In particular,after 15 minutes, Hydrogel A includes an aggregation of particles thatare not completely hydrated; in contrast, after 15 minutes Hydrogel B ishomogeneously hydrated. The media uptake ratio of both hydrogels wasdetermined at 5, 10, 15, 30, and 45 minutes following capsuledisintegration. The results, which are set forth in FIG. 3, show thatHydrogel B swells much more rapidly than Hydrogel A and, in particular,is significantly more swollen over the first 15 minutespost-disintegration. Both hydrogels reach equilibrium swelling at about30 minutes following disintegration.

Example 8 Determination of Swelling Kinetics

The hydration kinetics of Hydrogels A and B (Example 6) in SGF/water(1:8) were determined (i) using viscosimetry and (ii) by measuring themedia uptake ratio over time as described below.

(A) Viscometry

-   Apparatus:-   Rheometer, Discovery HR-1 by TA Instruments equipped with:-   Starch Pasting Cell with temperature control.-   Helical rotor (bob diameter 32.40 mm; bob length 12 mm).

Flow Peak Hold Test Parameters:

-   Angular velocity: 6.28 rad/s (velocity applied to the sample by the    motor at each measurement).-   Duration: 3600 s.-   Temperature: 37° C.-   Solution: SGF/Water (1/8) pH 2.1.-   Concentration of Hydrogels A and B: 1% w/w.

The results of this study are shown in FIG. 4, which is a graph ofviscosity versus time. The viscosity of Hydrogel B increases much morerapidly than that of Hydrogel A, and reaches a much greater value thanHydrogel A.

(B) Media Uptake Ratio versus Time

The media uptake ratios of Hydrogel A and Hydrogel B were determined asdescribed in Example 5(D) except that measurements were taken at 5, 10,20, 30 and 60 minutes. The results shown in FIG. 5 indicate thatHydrogel B absorbs SGF/water (1:8) more rapidly over the first 10 to 15minutes than Hydrogel A.

(C) G′ versus Time

This experiment was performed using the apparatus and method describedin (A) above, but with a frequency of 10 rad/sec. The results are shownin FIG. 6, which is a graph of G′ versus time for Hydrogel A andHydrogel B. Hydrogel B has a significantly higher G′ than Hydrogel A atall time points. This difference in G′ is particularly significant atearly time points.

Example 9 Comparison of Swollen Hydrogels to Masticated Food

G′ determined for 124 lots of crosslinked carboxymethylcelluloseprepared according to Example 3 (low viscosity CMC) and 36 lots preparedaccording to Example 2 (high viscosity CMC). In addition, the G′ of amasticated food bolus consisting of a Big Mac™ hamburger, an order ofFrench fries and 350 mL of a medium consisting of 50 mL pure SGF and 300mL of the soft drink Sprite™ was measured in triplicate. The G′ valueswere determined as described in Example 5, and the average G′ determinedfor each sample type is shown in Table 4 below.

TABLE 4 Sample Average G′ Low viscosity CMC 1050 Pa High viscosity CMC2070 Pa Masticated food 1957 PaThe results show that the hydrogels prepared with the high viscosity CMChave a G′ which is much closer to that of masticated food than thehydrogels prepared with lower viscosity CMC.

Example 10 Determination of Polymer Molecular Weight and PolydispersityIndex

The weight average molecular weight and polydispersity index of samplesof sodium carboxymethylcellulose (CMC) were determined using the methodset forth below. Data were analyzed using a computer with data analysissoftware.

Gel Permeation Chromatography Apparatus

-   1) Guard Column:-   Brand: Agilent Technologies PL-aquagel-OH Guard column-   Size: 50×7.5 mm (length×diameter); 8 μm (particles size).-   2) Column:-   Brand: Agilent Technologies PL-aquagel-OH Mixed-H-   Size: 300×7.5 mm (length×diameter); 8 μm (particles size).    Preparation of Aqueous Eluent-   1. In 1 L graduated cylinder pour 500 ml of purified water.-   2. Weigh 17 g±0.05 g of Sodium nitrate and pour it in the graduated    cylinder.-   3. Weigh 1.56 g±0.05 g of Sodium Phosphate Monobasic dihydrate and    pour it in the graduated cylinder.-   4. Add purified water in the cylinder up to 1 L.-   5. Insert a stirrer bar in the cylinder and cover it with parafilm.-   6. Put the cylinder on the magnetic stirrer and stir until complete    dissolution of the salt.-   7. Measure the pH of the solvent and adjust to pH 7±1 if necessary    with 0.2 N sodium hydroxide.-   8. Filter 200 ml of the eluent using a syringe filter (mesh size 0.2    μm) and store it in a covered beaker in order to prepare the sample    for GPC analyses.    Gel Permeation Chromatography    Calibration:-   Set the temperature of the chromatography apparatus to 35° C.-   Set up a ramp for the eluent flow up to 1 ml/min and allow the RID    to stabilize.-   Prepare Pullulan standards for calibration as follows:-   Dissolve each standard in the filtered eluent at 0.15% w/v,    according to the following sequence:-   667, 6000, 21700, 48800, 210000, 805000, 1330000, 2560000 [g/mol]    Allow the standards to completely dissolve in the eluent and inject    the standards one at a time. Create a calibration curve.

The stability of the apparatus is verified over time using the retentiontime of the Internal Standard: D-Sorbitol 182 g/mol (0.15% w/w in theeluent)

Analysis of sodium carboxymethylcellulose:

-   Each CMC sample is prepared by dissolving 0.015 g of CMC powder in    10 mL of eluent in a closed vial. The samples are prepared in    triplicate.-   Allow CMC samples to dissolve in the eluent by stirring overnight at    room temperature.-   Inject each sample.-   Data are analyzed using an interfaced computer and appropriate data    analysis software (Empower3, Waters Corporation) to determine M_(w)    and polydispersity index (integration algorithm: ApexTrack).    Results

The results of the analyses of three lots each of AQUALON 7H4FM and 7H3SXF are set forth in Table 5 below.

TABLE 5 Viscosity (cps, 1% Mw Polydispersity Sample in water at 25° C.)(Dalton) Index A. 7H4FM 9000 3.06 × 10⁶ 5.9 B. 7H4FM 8900 3.15 × 10⁶ 5.2C. 7H4FM 7600 3.16 × 10⁶ 6 D. 7H3SXF 2100 2.70 × 10⁶ 9.5 E. 7H3SXF 23202.69 × 10⁶ 8.5 F. 7H3SXF 2100 2.72 × 10⁶ 16.0These results show that the AQUALON™ 7H4FM samples have significantlygreater viscosity and Mw than the 7H3SXF samples. The 7H4FM samples alsohave a significantly lower polydispersity index, indicating the narrowermolecular weight distribution and greater molecular weight homogeneityof this material compared to the 7H3SXF samples.

Example 11 Determination of Swelling and G′ in Simulated IntestinalFluid

Preparation of Simulated Intestinal Fluid

Simulated Intestinal Fluid (SIF) Test Solution, known formally as‘Intestinal fluid, simulated TS (Test Solution)’, was prepared accordingto the method of United States Pharmacopeia 33-28NF (2010). Monobasicpotassium phosphate (6.8 g) was dissolved in 250 mL of water and then 77mL of 0.2 N sodium hydroxide and 500 mL of water were added to thissolution. 10.0 g of pancreatin was then added and the resulting solutionwas adjusted with 0.2 N sodium hydroxide or 0.2 N hydrochloric acid to apH of 6.8±0.1 and finally diluted with water to a volume 1000 mL.

The G′ and media uptake ratio in both SGF/water 1:8 and simulatedintestinal fluid (SIF) were determined for two lots of crosslinkedcarboxymethylcellulose prepared according to the method of Example 2(Hydrogel B) and two lots prepared according to the method of Example 3(Hydrogel A). The G′ and MUR in simulated intestinal fluid weredetermined as described in Example 5 except that simulated intestinalfluid was substituted for SGF/water 1:8. The results are shown in Table6 below.

TABLE 6 G′ G′ MUR MUR SGF/Water 1:8 SIF Material SGF/Water 1:8 SIF (Pa)(Pa) Hydrogel A 78 58 1336 977 (Lot 1) Hydrogel B 75 66 2221 1357(Lot 1) Hydrogel A 83 60 986 750 (Lot 2) Hydrogel B 70 60 2341 1734 (Lot2)The results show that materials produced using high viscositycarboxymethylcellulose have significantly greater G′ when swollen ineither SIF or SGF/water 1:8 compared to materials produced using lowviscosity carboxymethylcellulose. Surprisingly, while the MUR of the lowviscosity material in SGF/water 1:8 was slightly greater than that forthe high viscosity material, in SIF the two types of materials wereessentially equivalent. Notably, going from SGF/water 1:8 to SIF, theMUR decrease for the high viscosity material was significantly less thanthe decrease for the low viscosity material.

These results are important because the presence of swollen hydrogel inthe small intestine plays a fundamental role as far as mechanisms thataffect glycemic control, especially the creation of a diffusion barrierfor slowing glucose absorption by increasing the elasticity andviscosity of ingested food. In addition, higher elastic response of thesmall intestine content may contribute to achieving an effect similar tothat of a gastric bypass (Saeidi N, et al., Science 2013,341(6144):406-10).

Intestinal fluids have high ionic strength, which significantlydecreases the hydrogel swelling due to a decrease in the Donnan typeswelling contribution (see A. Sannino and L. Nicolais, Polymer, 46(13)4676-4685 (2005)). The Donnan contribution promotes hydrogel swelling bymeans of an osmotic pressure generated between the inside and theoutside of the hydrogel, allowing water to penetrate the hydrogel anddepends, in a linear fashion, on the difference in concentration ofionic charges between the inside and the outside of the hydrogel; thehigher the difference, the higher the Donnan contribution.

Hydrogels made from carboxymethylcellulose with high viscosity and lowpolydispersity have unexpectedly better hydration rates combined withhigher G′ compared to CMC-based hydrogels described in the prior art andalso have better combined G′/MUR performance in small intestine modelssuch as described in Example 5. This improved performance is surprisingconsidering the higher ionic strength of the small intestine fluids.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

We claim:
 1. A citric acid crosslinked carboxymethylcellulose, which isproduced by a method comprising crosslinking carboxymethylcellulosehaving a viscosity as a 1% (wt/wt) aqueous solution at 25° C. of greaterthan 6000 cps and a polydispersity index less than 8 with citric acid.2. The citric acid crosslinked carboxymethylcellulose of claim 1 in theform of particles which are at least 95% by mass in the size range of100 μm to 1000 μm with an average particle size in the range of 400 to800 μm and (ii) has a loss on drying of 10% or less (wt/wt).
 3. A citricacid crosslinked carboxymethylcellulose characterized by: (a) G′ ofabout 1200 to about 2000 Pa and a media uptake ratio of at least about90; (b) G′ of about 1400 to about 2500 Pa and a media uptake ratio ofabout 80 to 89; (c) G′ of about 1600 to about 3000 Pa and a media uptakeratio of about 70 to 79; (d) G′ of about 1900 to about 3500 Pa and amedia uptake ratio of about 60 to 69; (e) G′ of about 2200 to about 4000Pa and a media uptake ratio of about 50 to 59; or (f) G′ of about 2600to about 5000 Pa and a media uptake ratio of about 40 to 49; whendetermined on a sample of said citric acid crosslinkedcarboxymethylcellulose which (i) is in the form of particles which areat least 95% by mass in the size range of 100 μm to 1000 μm with anaverage particle size in the range of 400 to 800 μm and (ii) has a losson drying of 10% or less (wt/wt).
 4. The citric acid crosslinkedcarboxymethylcellulose of claim 2, having a tapped density from about0.5 g/mL to about 0.9 g/mL.
 5. The citric acid crosslinkedcarboxymethylcellulose of claim 4, having a tapped density from about0.65 g/mL to about 0.75 g/mL.
 6. The citric acid crosslinkedcarboxymethylcellulose of claim 3, which is produced by a methodcomprising crosslinking carboxymethylcellulose having a viscosity as a1% (wt/wt) aqueous solution at 25° C. of greater than 6000 cps and apolydispersity index less than 8 with citric acid.
 7. The citric acidcrosslinked carboxymethylcellulose of claim 4, wherein the viscosity isfrom 7800 to 11000 cps and the polydispersity index is from about 4 toabout
 7. 8. The citric acid crosslinked carboxymethylcellulose of claim1, wherein the viscosity is from 7800 to 11000 cps and thepolydispersity index is from about 5 to about
 7. 9. The citric acidcrosslinked carboxymethylcellulose of claim 1, wherein thecarboxymethylcellulose has a degree of substitution of about 0.65 toabout 0.95.
 10. The citric acid crosslinked carboxymethylcellulose ofclaim 1, wherein the carboxymethylcellulose is crosslinked with 0.05 to0.5% citric acid relative to the weight of the carboxymethylcellulose.11. The citric acid crosslinked carboxymethylcellulose of claim 1, inthe form of particles, wherein the particles are at least 80% by mass inthe size range of 100 μm to 1000 μm and the particles have an averageparticle size in the range of 400 to 800 μm.
 12. The citric acidcrosslinked carboxymethylcellulose of claim 1, having a loss on dryingof about 10% or less.
 13. A method for producing a crosslinkedcarboxymethylcellulose, comprising the steps of (a) preparing an aqueoussolution of carboxymethylcellulose having a viscosity as a 1% (wt/wt)aqueous solution at 25° C. of at least 6000 cps and a polydispersityindex less than 8, wherein the concentration of thecarboxymethylcellulose is at least 1% by weight relative to water, andan amount of citric acid from about 0.05% to about 0.5% by weightrelative to the weight of the carboxymethylcellulose; (b) agitating thesolution; (c) drying the solution to form acarboxymethylcellulose/citric acid composite; (d) comminuting thecomposite to produce composite particles; (e) heating the compositeparticles at a temperature of at least about 80° C., therebycross-linking the carboxymethylcellulose with the citric acid andforming the crosslinked carboxymethylcellulose.
 14. The method of claim13, wherein the concentration of the carboxymethylcellulose in step (a)is from about 4% to about 8% by weight relative to water, and the citricacid concentration in step (a) is from about 0.15% to about 0.3% byweight relative to the weight of the carboxymethylcellulose.
 15. Themethod of claim 14, wherein the concentration of thecarboxymethylcellulose in step (a) is about 6% by weight relative towater, and the citric acid concentration in step (a) is about 0.2% byweight relative to the weight of the carboxymethylcellulose.
 16. Themethod of claim 15, further comprising the steps of: (f) washing thecrosslinked carboxymethylcellulose of step (e) with water; and (g)drying the washed crosslinked carboxymethylcellulose.
 17. The method ofclaim 16, further comprising the step of: (h) comminuting thecrosslinked carboxymethylcellulose product of step (g).
 18. A method forpreparing a crosslinked carboxymethylcellulose comprising the steps of:(a) providing an aqueous solution consisting essentially of sodiumcarboxymethylcellulose having a viscosity as a 1% (wt/wt) aqueoussolution at 25° C. of at least 6000 cps and a polydispersity index lessthan 8, citric acid and water; (b) stirring the aqueous solution; (c)evaporating the water from the solution to produce acarboxymethylcellulose/citric acid composite; (d) comminuting thecomposite to form composite particles; and (e) heating the compositeparticles to a temperature of at least about 80 ° C. thereby producingthe crosslinked carboxymethylcellulose.
 19. The method of claim 18,further comprising the steps of: (f) washing the crosslinkedcarboxymethylcellulose of step (e) with water; and (g) drying the washedcrosslinked carboxymethylcellulose.
 20. The method of claim 19, furthercomprising the step of: (h) comminuting the crosslinkedcarboxymethylcellulose product of step (g).
 21. The method of claim 18,wherein the concentration of the sodium carboxymethylcellulose in thesolution of step (a) is from about 4% to about 8% by weight relative towater, and the citric acid concentration in the solution of step (a) isfrom about 0.15% to about 0.3% by weight relative to the weight of thesodium carboxymethylcellulose.
 22. The method of claim 18, wherein theconcentration of the sodium carboxymethylcellulose in the solution ofstep (a) is about 6% by weight relative to water, and the citric acidconcentration in the solution of step (a) is about 0.2% by weightrelative to the weight of the sodium carboxymethylcellulose.
 23. Acrosslinked carboxymethylcellulose produced by the method of claim 13.24. A pharmaceutical composition comprising a crosslinkedcarboxymethylcellulose of claim 1, and a pharmaceutically acceptablecarrier or excipient.
 25. The pharmaceutical composition of claim 24, ina form suitable for oral administration.
 26. The pharmaceuticalcomposition of claim 25, in the form of a sachet, tablet or capsule. 27.A method of treating overweight or obesity in a subject in need thereof,comprising the step of orally administering to the subject asatiety-inducing amount of the pharmaceutical composition of claim 25.28. A method of enhancing glycemic control in a subject in need thereof,comprising the step of orally administering to the subject an effectiveamount of the pharmaceutical composition of claim
 25. 29. A method oftreating diabetes in a subject in need thereof, comprising the step oforally administering to the subject an effective amount of thepharmaceutical composition of claim 25.